A proportional amplifier that provides a 4-20 mA signal or an amplifier that provides a 0-800 mA signal can also be used to control a motor-driven valve. When troubleshooting a motor-driven valve, one must be careful to identify the type of valve and amplifier being used. If the proportional amplifier is used, it's important to determine its span. One may need to refer to the technical information that is provided with the valve. If the valve and amplifier are proportional, one will need to try a variety of voltages or currents through its span to ensure that it will operate correctly.
The proportional amplifier will have a range for the input signal, usually 4-20 mA or 0-10 volts, and it will also have an output range. Another way to test the drive motor is to provide the maximum output signal that the amplifier normally provides from a different source such as a bench-type power supply. If the motor operates from the test power supply, one may assume the motor is operational. If the motor doesn't operate from the test power supply, one should check to see if it has end switches incorporated that may cause an open circuit.
