Where can I get the measurement units of the sensor data?

  • 2 September 2022
  • 3 replies

I'm working with the time series data for anomaly detections models and I would like to know the units of the sensor data. 

I found a master thesis based on the Open Industrial Data and for the variables selected for it; the author specifies the units: 


But from the data I downloaded with the SDK the tag VAL_23_KA_9101_M01_62C:Z.X.Value     does not have unit:



I looked into the meta data field an the engunits key is empty:

{'P&ID No': None, 'PLC': None, 'PLC tagname': None, 'Sensor type': None, 'Tag group': None, 'Tag type': None, '_replicatedInternalId': '4326942079596138', '_replicatedSource': 'akerbp', '_replicatedTime': '1593024714000', 'archiving': '1', 'compdev': '0', 'compdevpercent': '0', 'compmax': '28800', 'compmin': '0', 'compressing': '1', 'convers': '1', 'descriptor': 'PH 1stStg Comp Mtr Current', 'digitalset': '', 'displaydigits': '-5', 'engunits': '', 'excdev': '0', 'excdevpercent': '0', 'excmax': '600', 'excmin': '0', 'exdesc': '', 'external id': None, 'filtercode': '0', 'future': '0', 'instrumenttag': '23_KA_9101_M01_62C:Z.X.Value', 'location1': '1', 'location2': '0', 'location3': '1', 'location4': '1', 'location5': '0', 'pointid': '160068', 'pointsource': 'VLH_PCN1', 'pointtype': 'Float32', 'ptclassid': '2', 'ptclassname': 'classic', 'ptclassrev': '1', 'recno': '144568', 'scan': '1', 'shutdown': '0', 'sourcetag': '', 'span': '100', 'squareroot': '0', 'srcptid': '0', 'step': '0', 'tag': 'VAL_23_KA_9101_M01_62C:Z.X.Value', 'totalcode': '0', 'type': None, 'typicalvalue': '50', 'userint1': '0', 'userint2': '0', 'userreal1': '0', 'userreal2': '0', 'zero': '0'}

I also notice that the description field seems to indicate that the sensor in measuring current PH 1stStg Comp Mtr Current which should be in Amperes and not Power, as is refered in the thesis. 



Finally, I notice that there is a quite similar tag VAL_23-KA-9101-M01-62B:X.Value instead of  VAL_23_KA_9101_M01_62C:Z.X.Value which does has units: 


Are these two sensor measuring the same variable? 


The second case Where I want to know the units is for the motor data.  According to one of the infographics, all this sensors are from the  motor and gears system:





But unfortunately, none of the units for this sensor is available in the data from SKD


From a question in the old google groups community I got this image that seems to have the units for some of the sensors: 



But I don’t know that um means in this context, from the question it seems these sensors measure vibration, for what I have read this variable can measure in: “ units of displacement (peak-to-peak movement in mils or thousands of an inch), units of velocity (zero-to-peak in in./sec), or units of acceleration (zero-to-peak in gs)”


Best answer by Stig Harald Gustavsen 6 September 2022, 18:39

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I will go through the timeseries in OID, and update the ones missing units, but when it is motor (mtr) currents you can quite safely assume it is amperes [A].  You can also quite safely assume the temperature is in [°C], pressure gauge and absolute timeseries in [Bar], but some Pressure Differential Transmitters (PDT) usually have [mBar]

but for the vibration data, I’m not entirely sure, possibly micro-meter[µm] peak to peak vibration. 

But I’m yes aware that some of the timeseries are missing units, that was lost on AkerBP’s infrastructure between the SCADA system and the OSI-soft PI Historian system. And I have notified AkerBP of this, but I will do some curation of the timeseries we have in Open Industrial Data :)  But thanks for notifying us about this. 

Hi Stig, thanks a lot for the answer. One more related question, for this tag VAL_23_ZT_92538:Z.X.Value  that indicated the valve position. Which units can I assume?  and also is this at the input of the compressor? 


I’m looking to map the data of this  control valve


And also the tag labeled in the image, which does not have units: 




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Hi, very well spotted Luis.

The ZT is the position feedback from the positioner of a bigger valve, I think its the suction throttle valves position feedback witch is in [%] opening since it is a proportional control valve, and its the same for the anti-surge valve. and the same unit on the LV (Level Valve) out of the suction scrubber,  but this is not the feedback from the positioner but the desired value for the valve to have. so assume that the valve positioners does it job well, then we can assume that the desired valve position is the actual position of the valve. but as you see in the picture there are two level control valves in parallel. but timeseries related to control valves are usually their desired position or their actual position, all in [%].