INSTALLATION AND OPERATING INSTRUCTIONS
Troubleshooting
SKF Multilog On-line System IMx-16Plus
User Manual
Revision Letter A
41 (66)
NO: There is an open circuit in the cable. Repair/replace the cabling.
YES: There is an internal open circuit in the sensor or there is a bad/oxidised
contact. First, try cleaning the contact before replacing the sensor connector
and checking again.
2.9.3.2 Checking 4-20 mA channels
In case of unexpected measurement values, check the channel configuration
especially scale, zero level and choice of engineering units.
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.
Channels where the input signal is 4-20 mA, should have an SKF provided, 250-ohm
load resistor fitted, refer section
1. Identify the input terminals where the channel in question is connected to the
IMx-16Plus and verify that the correct resistor is installed. If all appears OK,
measure the DC voltage (V) across the channel input using a digital
voltmeter. Is the voltage within the range 0,5 to 5,5 V DC?
NO: If the correct resistor is being used, the current is outside the expected
range for a 4-20 mA signal.
If the measured voltage is below the voltage range, continue to step
If the measured voltage is above the voltage range, replace with another load
resistor and recheck. If there is no change, check that it is a 4-20 mA current
signal that is being applied to the input, as a problem external to the IMx is
most likely indicated.
YES: The current is (reasonably) within the expected range for a 4-20 mA
signal. Estimate the equivalent current by calculating as follows:
Equivalent current (mA) = (V * 1000) / 250
Does this agree, approximately, with the mA value it is believed the external
circuit is transmitting?
NO: Continue to step
YES: The circuit and connections appear OK, double check the channel
assignment and its configuration and if no reason for the measurement error
is found, contact TSG for advice.