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's 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.