What is RTD?

RTDs are made of metal wires, usually copper or platinum, that offer resistance to the flow of electricity. The RTD’s resistance changes when its temperature changes, allowing it to be used as a gauge for measuring heat. RTDs are considered to be more accurate than thermocouples as they have a linear relationship between resistance and temperature. RTDs are also less affected by electromagnetic fields than thermocouples.

RTD Working Principle

The full English name of RTD is “Resistance Temperature Detector”, so to be precise, it should be translated as “Resistance Temperature Detector”.

RTD is a special kind of resistor whose resistance value increases as the temperature increases and decreases as the temperature decreases. In industry, this feature is used for temperature measurement, so RTD is also commonly known as “thermal resistance”.

Not all metals are suitable for making RTDs. Materials that meet this characteristic need to meet the following requirements:

• The resistance value of the metal has a linear relationship with the temperature change energy;
• The metal is more sensitive to temperature changes, that is, the resistance change (temperature coefficient) caused by unit temperature changes is relatively large;
• The metal can resist fatigue caused by temperature changes and has good durability;

There are not many metals that meet this requirement. Common RTD materials are: platinum (Pt), nickel (Ni), and copper (Cu).

Take platinum thermal resistance as an example. According to the different resistance values, it can be divided into Pt50, Pt100, Pt200, Pt500 and Pt1000.

The numerical value in the name indicates the resistance value of the thermal resistance at 0°C.

For example: Pt100, indicating that the resistance value of the sensor at 0°C is 100Ω.
And Pt1000, it means that the resistance value of the sensor at 0 ℃ is 1000Ω.
The resistance value of RTD thermal resistance at different temperatures can be approximated by the formula: R=R0(1+αT).

in:
1) R0 represents the resistance value of RTD at 0℃;
2) a is called the temperature coefficient, which represents the change value of the resistance at unit temperature;
3) T represents the measurement temperature, the unit is °C;

According to the number of lead wires of RTD thermal resistance, RTD can be divided into two-wire, three-wire and four-wire.

The lead of the two-wire RTD is to directly lead out two wires at both ends of the resistor to the temperature measurement module. The temperature measurement module adopts the principle of bridge balance, and RTD is used as one arm of the bridge to measure.

A three-wire RTD can largely eliminate the influence of the sensor leads themselves on the measurement results. The detection accuracy is greatly improved compared to the two-wire system.

Resistance Temperature Detector advantages

No compensation line is required, and the price is cheap;
It can transmit electrical signals over long distances;
High sensitivity and strong stability;
Good interchangeability and high precision.

Disadvantages of thermal resistance:

Although thermal resistance is widely used in industry. But it requires power excitation.
Temperature changes cannot be measured instantaneously.
The temperature measurement range is limited and the application is limited.

What is Thermocouple?

Thermocouples, on the other hand, are made of two different types of metals that are joined together at the sensor end. The junction between these two metals produces a voltage that is proportional to the temperature difference between the junction and the measuring point. Thermocouples are less expensive than RTDs and can measure a wider range of temperatures. They are also faster at responding to changes in temperature.

Thermocouple Working Principle

A thermocouple is a temperature sensing element. It converts the temperature signal into a thermoelectromotive force signal and converts it into the temperature of the measured medium through an electrical instrument.

The basic principle of thermocouple temperature measurement is that two homogeneous conductors of different compositions form a closed loop. When there is a temperature gradient at both ends, a current will flow through the loop. At this time, there is a seebeck electromotive force – thermal electromotive force between the two ends. This is called the Seebeck effect.

The two homogeneous conductors with different compositions are the hot electrodes, and the end with the higher temperature is the working end. The end with the lower temperature is the free end. The free end is usually at some constant temperature.

According to the functional relationship between thermoelectromotive force and temperature, a thermocouple indexing table is made. The index table is obtained under the condition that the free end temperature is at 0°C. Different thermocouples have different scales.

When a third metal material is inserted into the thermocouple loop. As long as the temperature of both junctions of the material is the same. The thermoelectric potential generated by the thermocouple will remain constant. That is, it is not affected by the access of the third metal into the loop.

Therefore, when measuring the temperature of the thermocouple, the measuring instrument can be connected. After measuring the thermoelectromotive force, the temperature of the measured medium can be known.

Thermocouple Advantages:

1. High measurement accuracy: The thermocouple is in direct contact with the measured object and is not affected by the intermediate medium.
2. Fast thermal response time: Thermocouples are sensitive to temperature changes.
3. Large measurement range: thermocouples can measure temperature continuously from -40 to +1600 °C.
4. Reliable performance and good mechanical strength.
5. Long service life and easy installation.

Types and structures of thermocouples

Types of thermocouples Thermocouples include k type (nickel-chromium-nickel-silicon), n-type (nickel-chromium-silicon-nickel-silicon-magnesium), e-type (nickel-chromium-copper-nickel), j-type (iron-copper-nickel) , t-type (copper-copper-nickel), s-type (platinum-rhodium 10-platinum), r-type (platinum-rhodium 13-platinum), b-type (platinum-rhodium 30-platinum-rhodium 6) and so on.

Structural form of thermocouple: The basic structure of a thermocouple is a thermal electrode, an insulating material and a protective tube. Display instrument, recording instrument or computer and other supporting use. In field use, thermocouples suitable for various environments are developed according to various factors such as the environment and the measured medium.

Conclusions, which one should you use?

It really depends on the specific application and what is more important: accuracy or speed. If you need to measure very high or very low temperatures, a thermocouple is the better choice. If you need more accuracy, then an RTD is the way to go.

Read more about: What Is 0-10V Signal Output?

Temperature Measurement Solutions

Sino-Inst is Manufacturer of RTD & Thermocouples for temperature measurement. We supply more than 20 kinds of RTD & Thermocouples. 40% RTD, 60% Thermocouples.

RTD & Thermocouples for diesel fuel measurement are mainly used for temperature measurement of various meadium.

RTD & Thermocouples enable stable temperature measurement. This greatly meets the measurement needs of many applications.

Sino-Inst’s RTD & Thermocouples for temperature measurement, made in China. Having good Quality, With better price. Our temperature measurement instruments are widely used in China, India, Pakistan, the US, and other countries.

The entire team at Sino-Inst’s has received excellent training, so we can ensure that every client’s needs are met. For assistance with your product requirements, whether it’s a RTD & Thermocouples for temperature measurement, flow sensor, or other device, give us a call.

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The standard platinum rhodium 10-platinum thermocouple is used to realize the thermocouple temperature measurement value transfer and precise temperature measurement in the temperature range of 419.527~1084.62 ℃. The accuracy grades are first-class and second-class standards.

The standard platinum rhodium 30-platinum rhodium 6 thermocouple is used for the value transfer and precision temperature measurement of the current thermocouple in the temperature range of 1100~1500℃. The accuracy grade has the second-class standard.

First-Class Standard Thermocouple WRPB-1

Second-Class Standard Thermocouple WRPB-2

Second-Class Standard Platinum Rhodium 30-Platinum Rhodium 6 Thermocouple

Related Blogs

Sino-Inst, Manufacuturer for Temperature Transmitters, like: Armoured thermocouple, assembly thermocouple, explosion-proof thermocouple, etc.

Sino-Inst’s Temperature Transmitters, made in China, Having good Quality, With better price. Our Temperature measurement instruments are widely used in China, India, Pakistan, US, and other countries.

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How do you read a K type thermocouple table?

In the thermocouple chart, the first row and the first column are all temperature values.
The rows are incremented by 10 degrees per grid.
The columns are incremented by 100 degrees per grid.
The intersection of the row and the column is the thermoelectric potential value at the current temperature.

Take the S-type couple to read the thermoelectric potential value at 280 degrees Celsius for example: first find 200 degrees from the first column, and draw a straight line to the right.
Then find 80 degrees from the first line and draw a straight line down. Where the two lines meet, the thermoelectric potential value at 280 degrees is 2.141 millivolts.

Type K thermocouple chart

K Reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	397	798	1203	1611	2022	2436	2850	3266	3681
100	4095	4508	4919	5327	5733	6137	6539	6939	7338	7737
200	8137	8537	8938	9341	9745	10151	10560	10969	11381	11793
300	12207	12623	13039	13456	13874	14292	14712	15132	15552	15974
400	16395	16818	17241	17664	18088	18513	18938	19363	19788	20214
500	20640	21066	21493	21919	22346	22772	23198	23624	24050	24476
600	24902	25327	25751	26176	26599	27022	27445	27867	28288	28709
700	29128	29547	29965	30383	30799	31214	31629	32042	32455	32866
800	33277	33686	34095	34502	34909	35314	35718	36121	36524	36925
900	37325	37724	38122	38519	38915	39310	39703	40096	40488	40879
1000	41269	41657	42045	42432	42817	43202	43585	43968	44349	44729
1100	45108	45486	45863	46238	46612	46985	47356	47726	48095	48462
1200	48828	49192	49555	49916	50276	50633	50990	51344	51697	52049
1300	52398	52747	53093	53439	53782	54125	54466	54807

Type N thermocouple chart

N reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	261	525	793	1065	1340	1619	1902	2189	2480
100	2774	3072	3374	3680	3989	4302	4618	4937	5259	5585
200	5913	6245	6579	6916	7255	7597	7941	8288	8637	8988
300	9341	9696	10054	10413	10774	11136	11501	11867	12234	12603
400	12974	13346	13719	14094	14469	14846	15225	15604	15984	16336
500	16748	17131	17515	17900	18286	18672	19059	19447	19835	20224
600	20613	21003	21393	21784	22175	22566	22958	23350	23742	24134
700	24527	24919	25312	25705	26098	26491	26883	27276	27669	28062
800	28455	28847	29239	29632	30024	30416	30807	31199	31590	31981
900	32371	32761	33151	33541	33930	34319	34707	35095	35482	35869
1000	36256	36641	37027	37411	37795	38179	38562	38944	39326	39706
1100	40087	40466	40845	41223	41600	41976	42352	42727	43101	43474
1200	43846	44218	44588	44958	45326	45694	46060	46425	46789	47152
1300	47513

Type E thermocouple chart

E Reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	591	1192	1801	2419	3047	3683	4329	4983	5646
100	6317	6996	7683	8377	9078	9787	10501	11222	11949	12681
200	13419	14161	14909	15661	16417	17178	17942	18710	19481	20256
300	21033	21814	22597	23383	24171	24961	25754	26549	27345	28143
400	28943	29744	30546	31350	32155	32960	33767	34574	35382	36190
500	36999	37808	39426	40236	41045	41853	42662	43470	44278	45085
600	45085	45891	46697	47502	48306	49109	49911	50713	51513	52312
700	53110	53907	54703	55498	56291	57083	57873	58663	59451	60237
800	61022	61806	62588	63368	64147	64924	65700	66473	67245	68015
900	68783	69549	70313	71075	71835	72593	73350	74104	74857	75608
1000	76358

Type J thermocouple chart

J Reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	507	1019	1536	2058	2585	3115	3649	4186	4725
100	5268	5812	6359	6907	7457	8008	8560	9113	9667	10222
200	10777	11332	11887	12442	12998	13553	14108	14663	15217	15771
300	16325	16879	17432	17984	18537	19089	19640	20192	20743	21295
400	21846	22397	22949	23501	24054	24607	25161	25716	26272	26829
500	27388	27949	28511	29075	29642	30210	30782	31356	31933	32513
600	33096	33683	34273	34867	35464	36066	36671	37280	37893	38510
700	39130	39754	40382	41013	41647	42283	42922	43563	44207	44852
800	45498	46144	46790	47434	48076	48716	49354	49989	50621	51249
900	51875	52496	53115	53729	54321	54948	55553	56155	56753	57349
1000	57942	58533	59121	59708	60293	60876	61459	62039	62619	63199
1100	63777	64355	64933	65510	66087	66664	67240	67815	68390	68964
1200	69536

Type T thermocouple chart

T reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	391	789	1196	1611	2035	2467	2908	3357	3813
100	4277	4749	5227	5712	6204	6702	7207	7718	8235	8757
200	9286	9820	10360	10905	11456	12011	12572	13137	13707	14281
300	14860	15443	16030	16621	17217	17816

Type S thermocouple chart

S Reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	55	113	173	235	299	365	432	502	573
100	645	719	795	872	950	1029	1109	1190	1273	1356
200	1440	1525	1611	1698	1785	1873	1962	2051	2141	2232
300	2323	2414	2506	2599	2692	2786	2880	2974	3069	3164
400	3260	3356	3452	3549	3645	3743	3840	3938	4036	4135
500	4234	4333	4432	4532	4632	4732	4832	4933	5034	5136
600	5237	5339	5442	5544	5648	5751	5855	5960	6064	6169
700	6274	6380	6486	6592	6699	6805	6913	7020	7128	7236
800	7345	7454	7563	7672	7782	7892	8003	8114	8225	8336
900	8448	8560	8673	8786	8899	9012	9126	9240	9355	9470
1000	9585	9700	9816	9932	10048	10165	10282	10400	10517	10635
1100	10754	10872	10991	11110	11229	11348	11467	11587	11707	11827
1200	11947	12067	12188	12308	12429	12550	12671	12792	12913	13034
1300	13155	13276	13397	13519	13640	13761	13883	14004	14125	14247
1400	14368	14489	14610	14731	14852	14973	15094	15215	15336	15456
1500	15576	15697	15817	15937	16057	16176	16296	16415	16534	16653
1600	16771	16890	17008	17125	17245	17360	17477	17594	17711	17826

Type R thermocouple chart

R Reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	54	111	171	232	296	363	431	501	573
100	647	723	800	879	959	1041	1124	1208	1294	1381
200	1469	1558	1648	1739	1831	1923	2017	2112	2207	2304
300	2401	2498	2597	2696	2796	2896	2997	3099	3201	3304
400	3408	3512	3616	3721	3827	3933	4040	4147	4255	4363
500	4471	4580	4690	4800	4910	5021	5133	5245	5357	5470
600	5583	5697	5812	5926	6041	6157	6273	6397	6507	6625
700	6743	6861	6980	7100	7220	7340	7461	7583	7705	7827
800	7950	8073	8197	8321	8446	8571	8697	8823	8950	9077
900	9205	9333	9461	9590	9720	9850	9980	10111	10242	10374
1000	10506	10638	10771	10905	11039	11173	11307	11442	11578	11714
1100	11850	11986	12123	12260	12397	12535	12673	12812	12950	13089
1200	13228	13367	13507	13646	13786	13926	14066	14207	14347	14488
1300	14629	14770	14911	15052	15193	15334	15475	15616	15758	15899
1400	16040	16181	16323	16464	16605	16746	16887	17028	17169	17310
1500	17451	17591	17732	17872	18012	18152	18292	18431	18571	18710
1600	18849	18988	19126	19264	19402	19540	19677	19814	19951	20087
1700	20222	20356	20488	20620	20749	20877	21003

Type B thermocouple chart

B reference terminal temperature: 0℃, 10 degrees μν value

℃	0	10	20	30	40	50	60	70	80	90
0	0	-2	-3	-2	0	2	6	11	17	25
100	33	43	53	65	78	92	107	123	140	159
200	178	199	220	243	266	291	317	344	372	401
300	431	462	494	529	561	596	632	669	707	746
400	786	827	870	913	957	1002	1048	1095	1143	1192
500	1241	1292	1344	1397	1450	1505	1560	1617	1674	1732
600	1791	1851	1912	1974	2036	2100	2164	2230	2296	2363
700	2430	2499	2569	2639	2710	2782	2855	2928	3003	3078
800	3154	3231	3308	3387	3466	3546	3626	3708	3790	3873
900	3957	4041	4126	4212	4298	4386	4474	4562	4652	4742
1000	4833	4924	5016	5109	5202	5297	5391	5487	5583	5680
1100	5777	5875	5973	6073	6172	6273	6374	6475	6577	6680
1200	6783	6887	6991	7096	7202	7308	7414	7521	7628	7736
1300	7845	7953	8063	8172	8283	8393	8504	8616	8727	8839
1400	8952	9065	9178	9291	9405	9519	9634	9748	9863	9979
1500	10094	10210	10325	10441	10558	10674	10790	10907	11024	11141
1600	11257	11374	11491	11608	10725	11842	11959	12076	12193	12310
1700	12436	12543	12659	12776	12892	13008	13124	13239	13354	13470
1800	13585	13699	13814

Download: K thermocouple chart

The working principle of thermocouple (thermocouple principle)

What is a thermocouple?
This is to start with the principle of thermocouple temperature measurement. The thermocouple is a kind of temperature sensing element and a primary instrument. It directly measures temperature and converts the temperature signal into a term electromotive force signal. It is converted into a term electromotive force signal by an electrical instrument (secondary instrument). The temperature of the measured medium.

The basic principle of thermocouple temperature measurement is that two different components of material conductors form a closed loop. When there is a temperature gradient at both ends, there will be a current passing through the loop, and then there is Seebeck electromotive force-term electromotive force between the two ends. This is the so-called Seebeck effect.

Two homogeneous conductors with different compositions are term electrodes, the end with a higher temperature is the working end, and the end with a lower temperature is the free end, which is usually at a certain constant temperature. According to the functional relationship between term electromotive force and temperature, a thermocouple index table is made. The index table is obtained when the free end temperature is at 0℃. Different thermocouples have different index tables.

When the third metal material is connected in the thermocouple circuit, as long as the temperature of the two junctions of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, it will not be affected by the third metal in the circuit. Therefore, when the thermocouple measures the temperature, it can be connected to the measuring instrument, and after the term electromotive force is measured, the temperature of the measured medium can be known.

The working principle of thermocouple:

Two conductors with different components (called thermocouple wires or thermoelectrodes) are connected at both ends to form a loop. When the temperature of the junction is different, an electromotive force will be generated in the loop. This phenomenon is called the thermoelectric effect. And The electromotive force is called thermoelectric force.

Thermocouples use this principle for temperature measurement. One end that is directly used to measure the temperature of the medium is called the working end (also called the measuring end), and the other end is called the cold end (also called the compensation end). The cold end and the display instrument or When the matching instrument is connected, the display instrument will point out the thermoelectric potential generated by the thermocouple.

A thermocouple is actually a kind of energy converter, which converts heat energy into electrical energy. Use the generated thermoelectric potential to measure temperature. Regarding the thermoelectric potential of a thermocouple, you should pay attention to the following issues:

1. The thermoelectric potential of a thermocouple is a function of the temperature difference between the two ends of the thermocouple. It is not a function of the temperature difference between the two ends of the thermocouple;
2. The size of the thermoelectric potential generated by the thermocouple. When the material of the thermocouple is uniform, it has nothing to do with the length and diameter of the thermocouple, but is only related to the composition of the thermocouple material and the temperature difference between the two ends;
3. When the two thermocouple wires of the thermocouple have determined the material composition. The thermoelectric potential of the thermocouple is only related to the temperature difference of the thermocouple. If the temperature of the cold junction of the thermocouple remains constant, the thermoelectric potential of the thermocouple is only Single-valued function of working end temperature.

Sino-Inst, Manufacturer for Thermocouples, like: Armoured thermocouple, assembly thermocouple, explosion-proof thermocouple, etc.

Sino-Inst’s Thermocouples, made in China, Having good Quality, With better price. Our Temperature measurement instruments are widely used in China, India, Pakistan, the US, and other countries.

As two major contact temperature sensors: thermocouple and thermal resistance. Their names differ by only one word and both can be used as sensors for measuring object temperature.

The choice of thermocouple or thermal resistance should be judged according to the measured object environment. Many people are not sure what to choose. Therefore, it is necessary to fully understand the difference between thermal resistance and thermocouple temperature sensor when choosing a temperature sensor.

Extended reading: RTD vs. Thermocouple: What’s the Difference, and Which Should You Use?

Here, we list some temperature measurement ranges of thermal resistance and thermocouple sensors, and the thermoelectric potential and thermal resistance values of 100°C.

Thermocouple

• Platinum Guy 10-Platinum (Type S) (0-1300℃), T=100℃, E(100,0)=0.646mV.
• Platinum Guy 13-Platinum (R type) (0-1300℃), T=100℃, E(100,0)=0.647mV.
• Zhenming-Zhensi (K type) (0-1200℃) T=100℃E(100,0)=4.096mV.
• Zhenming-Constantan (Type E) (-200-760℃), T=100℃, E(100,0)=6.319mV

Thermal resistance

• Platinum thermal resistance (pt100) (-200-850℃), T=100℃, R=138.50Q
• Copper thermal resistance, (Cu50) (-50-150℃), T=100℃, R=71.4Q.

RTD vs Thermocouple difference

A thermocouple is a sensor that measures temperature. It is a temperature sensor like a thermal resistance. But the main difference between thermocouple and thermal resistance lies in:

1. The nature of the signal.

The thermal resistance itself is a resistance, and the change of temperature causes the resistance to produce a positive or negative resistance change; while a thermocouple produces a change in the induced voltage, which changes with the change of temperature.

2. The temperature ranges detected by the two sensors are different.

The thermal resistance generally detects the temperature range of 0-150 degrees. The highest measurement range can reach about 600 degrees (of course, negative temperature can be detected).

The thermocouple can detect a temperature range of 0-1000 degrees (or even higher). Therefore, the former is low temperature detection, and the latter is high temperature detection.

3. Different materials

From the material point of view, thermal resistance is a metal material. Metal materials with temperature-sensitive changes, thermocouples are bimetallic materials. Both two different metals.

Due to the change in temperature, a potential difference is generated at the two ends of two different metal wires.

4. PLC modules are different

The thermal resistance corresponding to PLC and the input module of thermocouple are also different, this sentence is no problem. But generally PLC is directly connected to 4-20ma signal, and thermal resistance and thermocouple are generally equipped with transmitter before they are connected to PLC. If you connect to DCS, you don’t need to use a transmitter! The thermal resistance is the RTD signal, and the thermocouple is the TC signal!

5. PLC also has thermal resistance module and thermocouple module, which can directly input thermal resistance and thermocouple signals.

6. Different prices

Thermocouples are available in J, T, N, K, S and other models. Some are more expensive than resistors, and some are cheaper than resistors. However, if the compensation wire is included, the comprehensive cost of the thermocouple is higher. Thermal resistance is a resistance signal, and thermocouple is a voltage signal.

7. Different measurement principles

The principle of thermal resistance temperature measurement is based on the property of the resistance of the conductor (or semiconductor) that changes with temperature. The measurement range is minus 00 to 500 degrees. Commonly used are platinum resistance (Pt100, Pt10), copper resistance Cu50 (minus 50-150 degrees).

The principle of thermocouple temperature measurement is based on the thermoelectric effect to measure temperature. Commonly used are platinum rhodium-platinum (graduation number S, measuring range 0~1300 degrees), nickel chromium-nickel silicon (graduation number K, measuring range 0~900 degrees), nickel chromium-constantan (graduation number E, measuring range 0 to 600 degrees), platinum rhodium 30-platinum rhodium 6 (grading number B, measuring range 0 to 1600 degrees).

RTD vs Thermocouple, how to choose?

The selection of thermocouple should be based on comprehensive considerations such as the use temperature range, the required accuracy, the use atmosphere, the performance of the measurement object, the response time and the economic benefits.

1. Selection of measurement accuracy and temperature measurement range

• When the operating temperature is 1300~1800℃ and the accuracy is relatively high, the B-type thermocouple is generally used;
• The accuracy is not high, and the atmosphere allows the use of tungsten rhenium thermocouples.
• Tungsten rhenium thermocouple is generally used above 1800℃;
• The operating temperature is 1000~1300℃, the accuracy is required and the high accuracy is available. S-type thermocouple and N-type thermocouple are available;
• Generally use K-type thermocouple and N-type thermocouple below 1000℃;
• Generally use E-type thermocouple below 400℃;
• T-type thermocouples are generally used for measurement at 250°C and negative temperature. T-type thermocouples are stable and have high accuracy at low temperatures.

2. The choice of atmosphere

S-type, B-type, and K-type thermocouples are suitable for use in strong oxidizing and weak reducing atmospheres. J-type and T-type thermocouples are suitable for weak oxidizing and reducing atmospheres. If a protective tube with better airtightness is used, the requirements for the atmosphere are not too strict.

3. Choice of durability and thermal response

Thermocouples with larger wire diameters have better durability, but their response is slower. For thermocouples with large heat capacity, the response is slow. When measuring a temperature with a large gradient, in the case of temperature control, the temperature control is poor. It requires a fast response time and a certain degree of durability, so it is more appropriate to choose an armored couple.

4. The nature and state of the measuring object to choose the thermocouple

The temperature measurement of moving objects, vibrating objects, and high-pressure vessels requires high mechanical strength. A chemically polluted atmosphere requires a protective tube. In the case of electrical interference, higher insulation is required.

Selection process: model-index number-explosion-proof grade-precision grade-installation and fixed form-protective tube material-length or insertion depth.

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Sino-Inst, Manufacuturer for Temperature Transmitters, like: Armoured thermocouple, assembly thermocouple, explosion-proof thermocouple, etc.

Sino-Inst’s Temperature Transmitters, made in China, Having good Quality, With better price. Our Temperature measurement instruments are widely used in China, India, Pakistan, US, and other countries.

Armored thermocouples are usually used in conjunction with display instruments, paperless recorders and regulators. It can measure the temperature of liquid, vapor and gaseous media and solid surfaces in the range of 0-1600°C during various production processes.

Place the thermocouple core wire and inorganic mineral insulating material in a metal sleeve. The stretched solid assembly that can be wound becomes an MI Cable.

The armored thermocouple cable made of thermocouple wire as the core is welded to form the measuring end and assembled with the relevant junction box. The thermocouple is called the armored thermocouple. Furnace thermocouples can be manufactured into insulated, grounded, and exposed-end types as required.

Furnace thermocouple-Solution for coal chemical gasifier

The gasifier is the most representative device of the coal chemical industry. Sino-Inst is based on the special conditions of the TEXACO gasifier and the Shell gasifier. It shares the special structure and material selection of the gasifier thermocouple and other professional knowledge. Help users solve special problems The problem of temperature measurement in the occasion.

Accurate measurement and strict control of temperature are the key factors to ensure the normal operation of the process. It will directly affect whether the process is carried out under ideal conditions. It will even affect the service life, safety production and environmental protection of the overall equipment.

The temperature measurement conditions of TEXACO gasifiers and Shell gasifiers in the coal chemical industry are extremely specific due to the gasifier body structure, internal medium, reaction process, and operating conditions. Therefore, the choice of the corresponding Furnace thermocouple also highlights its special importance and complexity.

The author relies on many years of rich experience. The representative and typical working conditions of TEXACO gasifier and Shell gasifier. As well as the selection principles and precautions of the corresponding thermocouples, which I will discuss with you. It aims to provide reference guidance and suggestions for coal chemical users.

1.TEXACO gasifier

① Operating conditions of TEXACO gasifier

Representative sites of TEXACO gasifiers include Ningxia Coal Group’s 250kt/a methanol plant, Shenhua Baotou and Inner Mongolia Jiutai Energy’s coal-to-olefin project.

The above site adopts the TEXACO rapid cooling process and the whole waste boiler process, which is the most advanced energy-saving process in the world.

TEXACO gasifier has special working conditions such as high temperature, high pressure, coexistence of oxidizing and reducing atmospheres, strong scouring, and sudden changes in temperature and pressure.

The operating temperature of the combustion chamber is 1350-1500℃, and the operating pressure is 2.5-8.7 MPa.

The flame gas contains CO, H2, CO2, H2O, CH4, Ar, N2 and H2S and other components.

The melting point of coal ash is 1310-1370°C.

The shell of the combustion chamber and the lining refractory bricks are likely to shear each other due to the different coefficients of thermal expansion.

The most important thing is that the scouring and abrasion in the gasifier is extremely serious, so the measuring point of the thermometer must be located 15-25mm away from the inner wall of the furnace wall.

However, it is difficult to ensure uniformity in the furnace wall during the masonry process. Coupled with the existence of scouring and wear in the furnace. The furnace wall will be inevitably thinned gradually during the production process.

②The performance requirements of TEXACO gasifier for Furnace thermocouple:

Due to the special working conditions of the above-mentioned TEXACO furnace, the temperature sensor must be able to withstand a high temperature of 1600°C and a high pressure of 8.7MPa.

It can resist the double corrosion of oxidizing and reducing gas at the same time.

It has an adjustable insertion length and a follow-up structure. When the inner lining changes in thickness and torsion and shear, corresponding structural changes can be made.

③Temperature measurement solution for TEXACO gasifier

In response to these requirements, the Furnace thermocouple is designed with special materials and structure. It satisfies the harsh requirements of the gasifier operating conditions for the temperature sensor. It is a kind of thermocouple special for gasifiers with adjustable anti-vibration, erosion resistance, anti-oxidation, and multi-stage leakage resistance.

First of all, the main structure of the Furnace thermocouple adopts the design concept of adjustable anti-vibration.

When the thickness of the gasifier wall lining changes, the Furnace thermocouple can be adjusted within the range of ±120mm through the shrinkable threaded sleeve. In order to achieve the measurement, the element is always maintained in the best position.

When the furnace shell and the inner lining are sheared, the universal rotating ball can be used to make the probe rotate with the inclination. And under the action of the limit guide tube and the correction damping spring.

Keep the probe always in the correct position in the center of the wall bushing. It prevents the thermocouple of the gasification furnace from being broken when the furnace wall is deformed.

Multi-stage leak-proof structure design. When the thermowell is damaged, it can prevent convection between the inside of the furnace and the outside through the sleeve. Safety hazards caused by high temperature conduction or even leakage in the furnace. Reflect safety awareness and environmental protection concepts.

Secondly, the Furnace thermocouple protection tube material adopts imported silicon carbide material made by pressureless sintering of sub-micron silicon carbide powder. The material has the dual characteristics of ceramic and metal and can be used reliably even at high temperatures exceeding 1750°C.

Its thermal conductivity is equivalent to stainless steel, 5 times that of alumina. Hardness is one of the high-performance materials second only to diamond. Ultra-fine crystals smaller than 10μm have been tested by helium gas leak detection.

The porosity is almost 0, which can effectively prevent H2 and CO from damaging the Furnace thermocouple wire through the pores on the tube wall. Ultra-high hardness and density make it have ideal wear resistance and long-term resistance to material erosion. It can work in oxidizing and reducing atmospheres and corrosive environments of strong acids and alkalis even at ultra-high temperatures.

2.Shell gasifier

At present, more than ten sets of Shell gasifiers have been introduced in China. Representative sites are Henan Kaixiang Methanol Project, Yunwei Group’s synthetic ammonia and Guangxi Liuhua coal gasification plants.

①Shell gasifier operating conditions characteristics

Conditions to ensure the normal operation of Shell gasifiers:

Neither can cause damage to the over-temperature of the vaporizer. It is necessary to consume the lowest amount of oxygen as much as possible. To achieve complete carbon conversion, temperature control is essential.

However, the structural characteristics of the Shell gasifier determines that the temperature of the gasifier cannot be directly measured. It can only be controlled by indirect methods.

An “annular space” is formed between the inner membrane wall of the gasification furnace and the outer shell. Hot syngas cannot escape into the “annular space”, causing the shell to overheat. Calculating the temperature in the furnace by measuring the temperature of the water wall in the “annular space” is the characteristic of Shell gasification furnace temperature measurement.

The temperature in the “annular space” is collected at multiple points, and each temperature measurement point is the key to understanding whether the gasifier is operating normally. If there is any abnormality, find and analyze the cause immediately. And deal with it in time, otherwise it will cause major damage to the gasifier.

②Shell gasifier performance requirements for Furnace thermocouples

Because the pulverized coal of Shell gasifier is 4MPa. It is combusted with O2 and steam in a gasifier at around 1500°C. And when it was sent to the coal burner, it was already under a pressure of 2MPa. Therefore, the thermometer is required to have a pressure resistance of not less than 2MPa. It also has emergency measures in case of overpressure, and can withstand a high temperature of 1500°C.

Because the Shell gasifier is composite equipment that integrates dynamic and static equipment, as well as combustion, reaction, heat exchange, and quenching processes. Therefore, it is required that the thermocouple used must be easy to install and remove, and easy to replace. Because of its complex structure and many control points, a multi-point thermocouple must be used.

③Shell gasifier temperature measurement solution

The design solution of the special Furnace thermocouple for the multi-point core-pulling and leak-proof Shell gasifier has solved the on-site requirements.

a. Multi-point thermocouples of different lengths (up to 6m) are used to measure the temperature of different control points in one fell swoop, using 3-point or 4-point thermocouples.

b. According to the characteristics of on-site installation, 4in (1in=25.4mm) No. 600 flange mounting parts are used. This part and the temperature measurement body are separable structures. The flange installation and fixing can be completed first. Then the temperature measurement body Installation with flange.

This solution allows the bulky flange to be installed at one time. In daily maintenance, only the main part needs to be replaced, which is convenient and quick. Closely combined with this structure is the independent replaceability of the core elements. Each measuring element is a detachable individual. If any one fails, it can be taken out and replaced separately. The maintenance cost and the quantity and expense of spare parts are reduced.

c. Due to the large amount of HCl in the medium in the furnace. Incoloy and Inconel alloys are often used in equipment manufacturing. In order to maintain a high resistance to high temperature and corrosion, the selection of Furnace thermocouple protection tube materials must all use Inconel600 alloy. Keep temperature measurement components , The material consistency of the mounting flange and the sealing sleeve.

d. The thermometer must have a multi-stage leak-proof sealing structure design. That is, each element must have a double-stage leak-proof device. When any temperature measuring element is damaged, due to the existence of leak-proof, the “annular space” The high temperature and high pressure airflow will not leak. It also guarantees the safety and environmental protection on-site requirements.

3.Furnace thermocouple installation instructions

①After the gasifier is shut down, consider the decompression effect of refractory materials and pressure vessels and the problems of thermal expansion and contraction. The pressure relief and replacement process of the gasifier is carried out slowly, and the furnace pressure should be basically reduced to atmospheric pressure and completely replaced.

After that, while the molten slag has not completely solidified, the gasifier thermocouple is drawn out of the furnace.

If the slag is solidified, the thermocouple ceramic sleeve cannot be pulled out, only the metal part at the back can be pulled out. The ceramic sleeve is usually driven into the furnace with a special tool.

②When installing a new gasifier thermocouple, put the assembled gasifier thermocouple on a special bracket. The bracket is placed on the wheeled trolley so that the gasifier thermocouple is exactly aligned with the gasifier thermocouple.

The equipment takes over in the middle. Slowly push the gasifier thermocouple into the furnace, about 10mm every 5 minutes. Protect the thermocouple from thermal shock.

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Sino-Inst’s Temperature Transmitters, made in China, Having good Quality, With better price. Our Temperature measurement instruments are widely used in China, India, Pakistan, US, and other countries.

A bimetallic stemmed thermometer is a simple but effective tool used in a variety of industries, including food, HVAC, medical, and automotive. It’s easy to use, requires no external power source, and is highly durable. In this guidebook, we’ll explain how a bimetallic stemmed thermometer works, its advantages and disadvantages, how to use it, and its various applications. So, whether you’re a professional or just curious about thermometers, you’ll find everything you need to know right here. Let’s get started!

Benefits of Bimetallic stemmed thermometer

(1) The thermoelectric potential is not disturbed. The thermoelectric potential of the bimetal thermometer is not disturbed by other factors. It has strong adaptability to different measurement environments.　

(2) The structure is diverse and can meet different measurement requirements. It can be used as electric contact bimetal thermometer, explosion-proof electric contact bimetal thermometer, bimetal thermometer with remote transmission, etc.

(3) The temperature response speed is fast, and there is strong sensitivity. At the same time, temperature changes are intuitive and can be displayed and recorded on site.

(4) Small size, convenient application, and strong temperature measurement reliability. Nominal diameter of dial: 60,100 (4 inch), 150 optional;

(5) It has a long service life, can be used in the temperature detection of chemical production for a long time, and has stable physical and chemical properties.

(6) Stable anti-corrosion performance. The application of bimetallic thermometers in chemical production often needs to be used in liquid and gas environments. It has a good anti-corrosion ability to protect pipes. It will not be affected by measurement conditions and cause corrosion problems that affect measurement quality.

(7) Strong pressure bearing. It has good pressure-bearing capacity, can be measured in different pressure levels, and has strong adaptability to measurement conditions.

(8) The conductivity is high. The temperature coefficient of resistance is small, and the thermoelectric potential has a linear relationship with the temperature, and the linearity is good.

Method 1: Ice water

1. Fill the container with ice cubes, and then top up with cold distilled water to form a watery slurry.

2. Insert the thermometer probe into the container, making sure not to touch the side.

3. The temperature should be 32°F (0°C) after 30 seconds. If not, the thermometer needs to be recalibrated. Record the difference and offset the thermometer as needed.

Method 2: boiling water

1. Boil a clean container of distilled water.

2. Once the water boils, insert the thermometer probe. Make sure again that the probe does not touch the side or bottom of the pot.

3. The temperature should be 212°F (100°C). Record the difference and offset the thermometer as needed. Note that the boiling point of water varies with altitude. Use this handy water boiling point calculator to find the temperature that suits your altitude.

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Sino-Inst, Manufacturer for Bimetallic stemmed thermometers, like Digital Thermometer/Transmitter, Digital Thermometer/Transmitter, explosion-proof thermocouple, etc.

Sino-Inst’s Bimetallic stemmed thermometers, made in China, Having good Quality, With better price. Our Temperature measurement instruments are widely used in China, India, Pakistan, the US, and other countries.

Temperature sensor transmitter is a combination of temperature sensor and temperature transmitter. It can be used in chemistry and medicine.

Thermocouple, thermal resistance and temperature transmitter of SBW series are the temperature transmitter units of on-site installation type in DDZ series instruments and they are used by matching with industrial thermocouple, thermal resistance. It uses dual-wire transmission mode(two conducting wires are used as the common transmission lines for power input and signal output).

It transforms the industrial thermocouple, thermal resistance signal into 4-20mA and 0-10 mA output signals which are linear with input signal and temperature signal. The transmitter can be directly installed in the junction box of the thermocouple and thermal resistance so as to form an integrated structure. As the temperature measuring instruments of new generation, it is widely used in metallurgy, petroleum, chemical industry, electric power, light industry, textile, food, national defense, scientific research and other industrial sectors.

The Difference Between Temperature Sensor Transmitter

A temperature sensor refers to a sensor that can sense temperature and convert it into a usable output signal. Temperature sensor is the core part of temperature measuring instrument, and there are many types. According to the measurement method, it can be divided into two categories: contact type and non-contact type.

Temperature transmitter uses thermocouple and thermal resistance as temperature measuring elementAfter measurement, the output signal is sent to the transmitter after voltage stability filtering, operational amplification, nonlinear correction, V/I conversion, constant current and reverse

The Function Of The Temperature Transmitter

A temperature transmitter is an instrument that converts a temperature variable into a standard output signal that can be transmitted.Mainly used for the measurement and control of temperature parameters in industrial processes.
The temperature current transmitter converts the signal of the temperature sensor into a current signal, and connects it to an auxiliary instrument to display the corresponding temperature.

Advantage Analysis

• High precision
• The range and zero point can be continuously adjusted from the outside
• Good stability
• Positive mobility can reach 500%, negative mobility can reach 600%
• Two-wire system, three-wire system, four-wire system
• Adjustable damping, overvoltage resistance
• Solid state sensor design
• No mechanical moving parts, less maintenance
• Light weight (2.4kg)
• Full series of unified structure, strong interchangeability
• Miniaturization (total height 166mm)
• The diaphragm material contact medium is optional
• Unilateral overpressure
• Low-pressure casting aluminum alloy shell
• Superior measurement performance, used for pressure, differential pressure, liquid level, flow measurement

Technical Parameter

1. input
Thermocouple: (two wire system), voltage: connect cable:sensor lead, maximum impedance 1.5k
Thermal resistance: (three wire system, four wire system), resistance measurement: connect cable: resistance compensation can reach 50.
2.output Isolated voltage 0.5kV instead of 2.5KV
3.Transmitter input options, accuracy and environmental temperature impact.

How Does A Thermocouple Transmitter Work?

Thermocouple or thermal resistance sensor will be converted into electrical signal by the temperature and then, the signal is sent to the input network of the transmitter which is consisted of zero adjustment circuit, a thermocouple compensation circuit and other related circuits. The signal after zero adjustment will be input to the operational amplifier for signal amplification. The signal after amplification will be output as 4 ~ 20mA DC after being processed by the V/I converter in one way; in another way, it will be displayed in gauge outfit after being processed by A/D converter.

There are two kinds of linear circuit in the transmitter, both of which adopt the feedback mode. The thermal resistance sensor is corrected by the positive feedback mode while the thermocouple sensor is corrected by approximation method of multiple-segment line. There are two kinds of display modes for the temperature transmitter of integrated digital display. The temperature transmitter displayed by LCD is output by the two-wire system while the temperature transmitter displayed by LED is output by the three-wire system.

1. Bimetal sensor：The bimetal consists of two pieces of metal with different expansion coefficients glued together. As temperature changes, material A will expand more than other metals, causing the metal plate to bend. The curvature of the bend can be converted into an output signal.
2. Bimetal rod and metal tube sensor：As the temperature rises, the length of the metal pipe (material A) increases,but the length of the unexpanded steel pipe (metal B) does not increase, so due to the change in position, the linear expansion of the metal pipe can be transmitted. Furthermore, this linear expansion can be converted into an output signal.
3. Sensor designed for liquid and gas deformation curve：When the temperature changes, the volume of liquid and gas will change accordingly.

Various types of structures can convert this expansion change into a position change, thereby generating a position change.

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