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User Guide
This flow transmitter 4 to 20 milliamp current output calculator provides a way to determine the output reading from the measured flow and flow transmitter range. A conversion scale graphic for each flow and 4-20mA current output range combination entered is also displayed below the calculated values.
Formula
This flow transmitter output calculator uses the following formula to calculate the output over a 4-20mA range:
Linear mA out = 4 + (16 x ((Rdg – Low Limit) / (High Limit – Low Limit)))
Parameters
Unit
Enter the unit used for measuring flow, e.g. m³/s, gpm, gallons per second, litres per minute, tons per hour, kilograms per day, etc…
Reading
This is the flow measured by the flow transmitter that you wish to convert to a 4 to 20 milliamp current output reading.
Low Limit
Enter the lowest flow that the flow transmitter will measure. For example zero would be a typical value for most flow transmitters, but you can also add negative (-) or positive (+) values as well. Please enter the value in the same flow units as specified for all other input values.
High Limit
Enter the maximum flow that the flow transmitter will measure.
Output Reading (mA)
This is the expected ideal flow transmitter current output signal in milliamps for the specified flow measurement.
Why does the flow meter need to output 4-20mA signal?
Flow meters are a kind of industrial products that are used a lot in the industry, and there are many types of flow meters. There are glass rotameters for on-site observation, metal tube rotameters with remote transmission, electromagnetic flowmeters, vortex flowmeters and so on.Most of the flowmeters choose 4-20mA signal output instead of 0-20mA signal, and do not choose pulse signal. In fact, there is a reason for this.
1. The voltage signal of the flowmeter is unstable, and it is simply interfered during long-distance transmission, while the current signal is relatively stable. Select the current signal during the transmission process, and select the voltage signal (voltage value range) for the detailed control of the control instrument (accumulator) and the distributed control system.
The signal in the range of 2.0-20mA cannot be distinguished from the fault signal. Less than 4mA indicates that the line is faulty or there is suspected zero drift. The birth of the two-wire meter promoted the change of specifications, and the new specification of current signal is 4-20mA.
3. The two-wire sensor is set to the specification of 4-20mA, during which a current of 0-4mA is required to provide the minimum operating current of the sensor itself. If you choose 0-20mA, when the signal is very small, the sensor will not get satisfactory working energy.
4. In fact, in the signal of about 4-20MA, the DCS system usually considers more than 20.2 mA and less than 3.8 mA as a fault.
