Sensor Calibration

 

 

Because the H2 sensors use thermal conductivity to quantify the %H2 in the gas sample, how the gas is presented to the sensor affects its calibration and resulting accuracy.  The in-situ H2 analyzer does not allow sample gases to flow past the H2 sensor.  Therefore, the calibration must be performed in a similar way.  The flow-through H2 analyzer requires that flows past the H2 sensor be similar to flows during normal operation to maximize accuracy of the sensor.  The setup and calibration methods are detailed below.

 

Additionally, the gas sensor must be calibrated at both the low end and high end of the measured gas composition range to ensure accurate readings.  Never perform a span calibration without first performing a zero calibration.  Performing only a zero or span calibration will cause the sensor to give an erroneous reading.  SSi suggests that this device should be calibrated on a routine basis, such as once a year or as prescribed by the user’s quality system requirements.

 

Connect the gas to the “Cal Gas Inlet” on the side of the SGA enclosure and open the valve.  It is recommended to let everything (gas and SGA) sit for approximately thirty minutes to allow the temperature to achieve equilibrium. 

 

To perform a sensor calibration, make sure that the system is set up to flow both zero gas (with 0% of the gas the sensor is designed to detect) and span gas when needed. The gases should be “Certified Primary Standards” or equivalent accuracy. Then follow these steps.

 

  1. Note the percentages of the sensor gas in each gas source (zero and span).

  2. Ensure that the system is purged of any latent gas.

  3. Flow the zero gas until the gas reading on the web page stabilizes.

  4. Enter the target gas concentration in the “Enter gas concentration (%)” field.

  5. Press “Calibrate”. A Calibration Timer will count down.

  6. Once the Calibration Timer has counted down, the zero value will be calibrated.

     

NOTE: The remaining steps for the span gas will be very similar to the steps performed for the zero gas calibration.

 

  1. Ensure that the system is purged of any latent gas.

  2. Flow the span gas until the gas reading on the web page stabilizes.

  3. Enter the target gas concentration in the “Enter gas concentration” field.

  4. Press “Calibrate”. A Calibration Timer will count down.

  5. Once the Calibration Timer has counted down, the span value will be calibrated.