As transducers age, their original calibrations drift, becoming less reliable due to repeated loading and unloading, ageing components, and environmental conditions. Temperature is an important factor in the calibration process as this has a strong effect on how transducers behave which is explained here. Ideally, a transducer should be calibrated at the temperature that it will be used at.
The goal of calibration is to minimise any measurement uncertainty by ensuring the accuracy of test equipment. Calibration quantifies and controls errors or uncertainties within measurement processes to an acceptable level.
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How often should I re-calibrate my transducers? The best practice is for transducers to be calibrated annually. However, this is dependent on the acceptable level of drift. |
A calibrated source that measures the same parameter as the transducer is required for re-calibration to be conducted.
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Calibrating a transducer using
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Connect the pore pressure transducer and set the sensitivity value to 1 and change the units to mV.
Unsure of “Transducer Full Scale”? Start with 10000mV, then apply the maximum pressure possible to the transducer. The value output by the transducer at its maximum pressure is its full-scale output.
Connect the pore pressure transducer to a calibrated pressure source and set the pressure to 0. Note the reading in mV.
These increments depend on the pressure rating of the transducer but an example for a 1Mpa transducer would be 0,100,200,300,400,500,600,700,800,900,1000. Note the reading in mV for each of these pressures.
Once at 1000kPa, you will have to repeat the increments until reaching 0 again to measure hysteresis (900,800,700,600,500,400,300,200,100,0 and note the mV reading for each pressure)
Plot this information and the gradient of this graph is your new sensitivity value. Applied pressure vs mV measured (this is your sensitivity as the units for this is kPa/mV).
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GDSLAB
Please refer to Helpsheet 142 - Entering new transducer calibration data
Pressure controllers: using our FieldCal software tool to re-calibrate a
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controller
First, “Connect” to your GDS controller by selecting the controller with the correct serial number from the drop-down box, then “Begin” calibration“Begin calibration”.
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You will then be met with this screen, select “Least Squares Calculator”1“Least Squares Calculator”.
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For a 3MPa controller, the following pressure intervals are only an example of what you can choose. Set the pressure of the reference to 0, type 0 in the “Reference “Reference (kPa)” 3 box and then select “Add”4“Add”. This will create the first calibration point. Repeat this for each pressure interval to the pressure limit and then go back down to 0.
The reference pressure is matched with the counts (ct) of the controller and a line is plotted to determine what pressure to display depending on the counts. For example, a two-point calibration matches 0kPa to 0ct and 1000kPa to 1000ct, this line will then interpret 371ct as 371kPa.
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Once finished. Select “Calculate “Calculate Least Squares Fit”5Fit”, this will provide you with the “Correlation Coefficient”6“Correlation Coefficient”, the closer this value is to 1 the better as this is the linearity of the calibration. Then “Save”7 “Save” the calibration, select “Use”8 “Use” and then select “Store Calibration Permanently”2“Store Calibration Permanently”. Info
AdvDCS V2 (Calamari) systems
To re-calibrate my transducers? The best practice is for transducers to be calibrated annually. However, this is dependant on the acceptable level of drift.transducers in systems based on AdvDCS V2 devices, please refer to the following page:
214 GDS Helpsheet - Change, update or create transducer calibrations in AdvDCS V2-based systems