What is the maximum load I can connect to the output of a 2-wire transmitter?
Unlike a 4-wire transmitter, the maximum load that can be connected to a 2-wire transmitter is dependent on the power supply used to power the output current loop and the loop voltage drop of the 2-wire transmitter. The 2-wire transmitter has a minimum source voltage and a maximum source voltage. The maximum output load would be realized using the maximum output source voltage. A 24 Vdc supply is most often used. The general formula is: Max RL=(Vss – LVD) / 0.02 A Where RL is the maximum load, VSS is the DC power supply voltage, and LVD is the loop voltage drop. All 2-wire transmitters have a Loop Voltage Drop specification. For example, the T713 RTD input transmitter has a loop voltage drop of 12 V. If a 24 Vdc power supply is used, what is the maximum load that can be connected to the output loop? Using the above formula the maximum load is 600 ohms.
