Tuesday 28 September 2021

Trouble-shooting fluctuating measurements.

Some measurement systems, like those monitoring pH, are very sensitive and prone to interference. Small current or voltage surges can cause large fluctuations in readings.

The connections at the back of
Microlink 751 data acquisition unit
Here are some simple tests to follow to determine the cause of the errors. The Microlink 751 multi-function USB unit is taken as an example but many of the tips also apply other systems. Work through the tests one-by-one, eliminating sources of error as you go.

1. Check that the Microlink is working properly. First remove other factors in the system that might be causing the problem, then check the Microlink itself.

    (a) Remove any power signal conditioner. This provides surge protection and noise filtering. It should remove interference from other equipment but a faulty one could cause its own problems.
    (b) Move the Microlink to another location. If you are using it in a laboratory for example, take it home.
    (c) Connect the Microlink to a different laptop running on battery power, not on mains power.
    (d) Now you can test whether the Microlink is the source of the noisy, fluctuating, data. Connect together the first positive input pin, the first negative input pin and the 0 V input pin. With the Microlink 751 these inputs are on pins 20, 1 and 19. You could use paperclips to connect the three pins. Leave all other inputs unconnected.
The Microlink is now shorted out: if it is working correctly it will produce a reading of zero. If not the fault lies with the unit and Technical Support should be contacted and the unit returned. If the reading is zero then the problem is very unlikely to be caused by the Microlink and you can go on to step 2.

2. Once the DAQ unit has been eliminated as the source of the fault, the power supply to the computer should be tested. Plug the laptop into the mains - the reading should still be zero.

3. Reconnect any power signal conditioner. Again, check that the reading is zero.

4. The sensors should be tested one-by-one. For example, place a pH probe in a known solution and see if the reading is as expected. Keeping the signal wires short and far away from electrical machinery helps reduce noise. The electrodes may also require cleaning. electrodes.

5. Move everything back to the original location. If the readings become erratic go through the tests again.

6. Disconnect from the laptop and connect to the original computer. Again, if you now get noisy readings repeat the tests. 7. Finally make the measurements in a real situation.

Discovering at which stage the problem occurs will allows the identification of the source and the taking of remedial action.

@DataAcquisition #PAuto #Calibration

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