SKF Multilog IMx-S Series User Manual page 31

Confirm that the signal applied is a 4-20 mA and not for example 0 to 20 mA. Also, be
aware that some 4-20 mA devices will set their outputs low (typically 2.9 mA) or high
(typically 21 mA) to signal a sensor/circuit failure. In such circumstances the output
current will be different to the source, measurement value.
1. Identify the input terminals where the channel in question is connected to the IMx-S
and disconnect one signal wire from the terminal/connector and recomplete the
circuit using a DMM set in current measurement mode. Is the measured current
within the expected range, 4 to 20 mA DC?
YES: Skip to step 2.
NO: This indicates a fault within the sensor loop, IMx load resistor or loop power
2. Does the measured mA current reasonably agree with the expected value from the
sensor or system providing the signal?
YES: Problem appears to be related to the IMx (hardware, installation or
NO: Recheck all loop wiring and where possible for test purposes, replace the
Checking analogue input channels
A alogue i puts efe to othe oltage i puts such as voltage sources or powered
voltage sensors rather than accelerometers, eddy current probes or 4-20 mA signals. In
case of unexpected measurement values, check the channel DIP switch settings and the
configuration especially scale, zero level and choice of engineering units. Ensure that the
cable check function enable/disable setting is appropriate for the signal applied.
1. Identify the input terminals where the channel in question is connected to the IMx-S
and verify that the connections are correct. If all appears OK, measure the DC
voltage across the channel input using a digital voltmeter. Is the voltage as expected
for the connected signal type?
NO: Continue to step 2.
YES: The sensor circuit and cabling appear essentially OK, double check the
If the measurement is AC, it may be necessary to substitute another sensor or simulate a
signal to effectively test the loop.
2. Disconnect the signal wire from terminal A and recheck the DC voltage between
that and the common terminal, B. Is the voltage now as expected, for the connected
signal, type?
SKF Multilog On-Line System IMx-S
User Manual – Revision S
supply. Recheck DIP switch settings and all loop connections. If the loop is IMx
powered, disconnect the wiring to the Pwr terminal and check the voltage
between Pwr and A terminals is around 24 V DC. In case of continued
difficulty, contact TSG for advice and further information, advising them of the
tests undertaken so far and details of the current loop being connected.
configuration). If on rechecking the aspects advised above, no reason for the
measurement error is found, contact TSG for advice.
sensor or loop source by something that will provide a known, fixed current
output, then retest. In case of continued difficulty, contact TSG for advice and
further information, advising them of the tests undertaken so far and details
of the current loop being connected.
channel assignment and its configuration. If the measurement is DC and no
reason for the measurement error is found, contact TSG for advice.
Troubleshooting Guide
Sensor circuits
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