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j) Measuring DC-Loop Current “%”
Loop current measurement is performed for diagnosis and troubleshooting for current interfaces, such as
PLC controls or sensor systems in industrial sensor and control lines. Current interfaces are standardised
and operated at a current of 4 - 20 mA and a max. voltage of 24 V/DC. The DMM indicates this area as
percentage of the loop current. The measured range is from 4 mA to 0% to 20 mA = 100%.
When the Measured value of 0% (4 mA) is undercut, the display shows “LO”. This means that the inter-
face is interrupted or down.
When the Measured value of 100% (20 mA) is exceeded, the display shows “HI”. This may provide infor-
mation on a defective sensor or signal converter.
Before connection and after measuring, always power down the switch.
Proceed as follows to measure the loop current:
-
Turn on the DMM and select measuring range “Hz%”.
Press “SELECT” button to switch measurement
functions. The symbol for DC loop current measuring in
% now appears in the display. Pressing this button again
takes you to the first measuring function etc.
-
Plug the red measuring line into the mAµA% measuring
jack. Plug the black measuring line into the COM socket.
-
Now connect the two test prods in series with the object
to be measured (power loop, sensor circuit etc.); the dis-
play indicates the polarity of the measured value together
with the currently measured value.
When a minus “-” appears in front of the measured
value, the measured voltage is negative (or the
measuring lines have been mixed up).
-
After measuring, remove the measuring lines from the
measured object and turn the DMM off.
Summary of Contents for VC870
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