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Calibration and verification

Many conductivity sensors on the market are big and bulky or probes with separate evaluation units that require matching and calibration in the field. ifm's LDL conductivity sensor is an all-in-one transmitter and does not require calibration in the field prior to use.

Factory calibration

Each conductivity sensor is factory calibrated during production to offer good performance out of the box.

  • Sensors cycle through calibration stations to adjust the sensor at different temperatures and conductivity ranges.
  • The final calibration bath is measured against a reference sensor. Information from this bath can be found in the factory certificate.
  • Download a free factory certificate from our website. Be sure to have the serial number of the sensor to enter.
  • The certificate also includes accuracy of the digital measurement. 

Field calibration

ifm conductivity sensors come ready to use out of the box but can also be adjusted in the field for specific media, reference temperatures, or to match known concentration curves. The two main parameters that can be adjusted to match a known value or reference sensor are the Calibration gain [CGA] and Temperature compensation [T.Cmp]

Calibration gain [CGA] adjusts the measurement curve of the sensor to match the conductivity of a known value at a given reference temperature.

  • The gain can be adjusted from 80 to 120% of the measured value and it is calculated by dividing the known value by the measured value. 

 

 

Temperature compensation [T.Cmp] adjusts the rate of change the conductivity changes as medium temperature changes.

  • The compensation can be adjusted from 0 to 5% of the measured conductivity value.
  • The temperature compensation value can be found on chemical medium datasheets or by the formula:
    • [T.Cmp]  =  (C2 - C1)  ÷  C1 (T2 - T1)  x 100  

Adjusting the CGA and T.Cmp provides the highest accuracy of the measured conductivity. Depending on your application, these adjustments may not be necessary. 

Adjusting calibration gain [CGA]

LDL2xx sensors

1 Maintain calibration solution at the reference temperature.
2 Set sensor temperature compensation [T.Cmp] parameter to 0% and dAP = 0. Download settings to sensor. 
3 Insert sensor into calibration fluid** and make sure media temp is stable at reference temperature. 
4 Adjust calibration gain [CGA] percentage up/down from 80…120% to match conductivity of calibration solution. CGA = known conductivity of calibration solution / measured value * 100. Enter this new % value for the calibration gain [CGA] parameter. 
5 Enter reference temperature [rEF.T] of the process media if known, otherwise use default. 
6 Return temperature compensation [T.Cmp] parameter to desired % (default 2%) and dAP = 1 
7 Download the changes to the sensor. 

**Alternatively, the sensor can be adjusted while installed using the above process to match the measurement to that of an existing device which has recently been calibrated. 

LDL100 sensors

Since the LDL100 is not a traditional conductivity with a fixed cell constant, the measured conductivity is influenced by the installed environment. The sensor accuracy stated on our datasheets include variability from sensor to sensor as well as variabilty due to installation. By eliminating the variability due to the installed environment, adjusting the CGA will significantly improve measurement accuracy.

  • Method 1: Adjustment strictly based on pipe size is easy to do based on the table below.
  • Method 2: For best accuracy follow the procedure laid out below with a calibration medium.
  • Does not apply to the LDL2xx which uses an inductive (toroidal) technology. Refer to the Technology page for more on the differences between these products.
Method 1: CGA adjustment by pipe size
Installed pipe size Calibration gain (CGA)
1-1/2" 96%
2"  97%
3" 100%
> 3" / tank 107%
Method 2: CGA adjustment using calibration medium
1 Install the sensor in the application or in same size pipe section to replicate the installation environment. Sensor accuracy is highly influenced by installation.
2 Maintain calibration solution at the reference temperature (typically 25 °C.
3 Set sensor temperature compensation [T.Cmp] parameter to 0% and dAP = 0. Download settings to sensor. 
4 Flow calibration medium through the system or insert pipe section into the medium. 
5 Adjust calibration gain [CGA] percentage up/down from 80…120% to match conductivity of calibration solution. CGA = known conductivity of calibration solution / measured value * 100. Enter this new % value for the calibration gain [CGA] parameter. 
6 Enter reference temperature [rEF.T] of the process media if known, otherwise use default. 
7 Return temperature compensation [T.Cmp] parameter to desired % (default 2%) and dAP = 1 
8 Download the changes to the sensor. 

Adjusting temperature compensation [T.Cmp]

For all LDL sensors

1 Set [T.Cmp] to 0% and [dAP] to 0 and download the change to the sensor.
2 Measure conductivity (C1) at temperature (T1), making sure temperature is stable.  
3 Change the medium temperature, wait until it is stable, and measure conductivity (C2) at new temperature (T2).
4 [T.Cmp]  =  (C2 - C1)  ÷  C1 (T2 - T1)  x 100 . Enter this new value for [T.Cmp}. 
5 Return temperature compensation [T.Cmp] parameter to ON and dAP = 1 and download the change to the sensor.