One of the conductivity measurements is based on the principle of an induction of a transformer. An AC voltage generator controls the primary side of the transformer. The liquid flows through the channel bore in the measuring head and forms a conductor loop (as most of the liquids are good conductor of electricity), which links the primary side of the transformer and the secondary side of the transformer.
Built-in around the hole are two coils; a primary coil supplied with an AC voltage and a secondary coil, which picks up a small signal through the media inducted voltage. The size of this voltage is dependent on the conductivity of the media. This signal is handled and amplified in the electronics to a linear analogue 4…20 mA output signals.
Also built into the body is a Pt100 sensor placed in the tip of the sensor. This is measuring the media temperature to enable temperature compensation of the conductivity signal, which is very temperature dependent. The Pt100 sensor signal also features as a separate analogue 4…20 mA output signals.
The measuring cell is a homogeneous sealed body. Through the body is a hole, through which the media is flowing as shown below
Calibration of conductivity transmitter
1.Put the cell constant as provided in the data sheet of sensor or sticker in the probe will be of a value like 02.7 (two point seven).Also take the transmitter to manual option this overrides the temperature effects
2.Enter the value of model of transmitter (for Rosemount 1066 it will be a model number like 228-torroidal sensors)
3.Put range in the transmitter as per your requirement like 0 to 20000 micro Siemens/cm
4.Remove the sensor from the pipe
5.Select measure conductivity option
6.The go to calibration option
7.Again enter to in process calibration
8.Clean the sensor with DM water
9.Turn off automatic temperature compensation in the transmitter. This eliminates error in the cell constant
10.Place the sensor in the standard solution like 1000 micro Siemens/cm solution
11.Wait for stability
12.Enter the value 1000 in transmitter and press enter key
13.Screen will be showing calibration under progress
14.After some 5 to 6 seconds , calibration completed will be shown in the transmitter
15.Remove the sensor and place it in the line and line up the transmitter
N.B: For zero calibration (in case if the transmitter is showing a negative value), remove the sensor from line and keep it in the open atmosphere, go to zero calibration option in the transmitter and enter zero calibration; the screen will be showing calibration under progress. After 5 to 6 seconds the transmitter will be showing calibration completed. Keep the transmitter in the process line and now the transmitter will be showing the process value and also if continuous error or temperature error is showing in the screen then go to diagnostic and ensure that it is turned off
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