Control Unit Model 20-35-Nm-F Check Procedure; Control Unit Model 20-35-Nm-Din Check Procedure - Thermo Scientific 20-35-NM-F User Manual

4.2

Control Unit Model 20-35-NM-F Check Procedure

1. Check the power supply voltage. Make sure the AC voltage selector SW4 is set to the
proper voltage. The proper voltage must be present between the HOT and NEUT
terminals.
2. Check the state of the "Probe Fault" relay K2 and (red) indicator LED 2. If the probe is
open-circuited, or the probe cable is shorted, the LED 2 is ON and relay K2 energized.
3. With the probe cable connected, measure the DC voltage across sensor terminals 1 and
2. The measurement should be between 18 and 23 volts.
4. Remove the probe wires from terminals 1 and 2. The "Probe Fault" relay K2 must be
energized and LED 2 is ON should indicate a probe fault has occured (open-circuited or
the cable is shorted).
5. With the probe cable still disconnected, measure the voltage at probe terminals 1 and 2.
The measurement should be greater than 20 volts DC.
4.3

Control Unit Model 20-35-NM-DIN Check Procedure

1. Check the power supply connection. Make sure the input power wires are connected to
the correct inputs on terminal block M1 and that they match the actual AC power
supplied to the unit.
2. Check the state of the "FAULT LED" (red). If the probe is open-circuited or the probe
cable is shorted, this led is ON.
3. With the probe cable connected, measure the DC voltage across sensor terminal block
M4 (terminals 1 and 2). The measurement should be between 18 and 23 volts.
4. Remove the probe wires from terminal block M4 (terminals 1 and 2). The "FAULT
LED" must be ON.
5. With the probe cable still disconnected, measure the voltage at probe terminal block M4
(terminals 1 and 2). The measurement should be greater than 20 volts DC.
4-2