Are you experiencing incorrect or unexpected readings? These tips will help you find the cause.
- Make sure the temperature is properly calibrated. If the temperature has been recalibrated at some point and is incorrect, there will be a big measurement discrepancy.
- Verify the slope. The slope should be between 1.5 and 2.2 If the number is outside this range the calibration was performed incorrectly (sensor was possibly not at thermal equilibrium at the time of calibration, the sensor was not dry, or was not placed over a bucket of water, or sensor was not rebuilt properly leading to an error).
- Most handheld portable units do not have salinity compensation. If you are comparing reading to a grab sample from a portable unit, you should TURN OFF salinity compensation in the menu otherwise you will never have an agreement.
- When you HOLD DOWN the RIGHT-HAND BUTTON you will see the RAW mV coming from the sensor. If you can provide us with this number and the ppm value, we divide this by the ppm value to obtain the slope. This is the best way to troubleshoot a raw value without any corrective errors affecting the reading.
Other tips:
- Temperature plays a vital role in accurate calibration therefore sufficient time must be allowed for the temperature and sensor reading to be fully stabilised (reach equilibrium) in this condition to ensure a good calibration
- Always use Automatic Temperature Compensation by default. Errors in the temperature compensation at calibration can cause exponential errors in subsequent in-tank readings
- We recommend you use Automatic Calibration rather than manual calibration. This can be initiated by simultaneously holding the Up & Down keys until the display flashes CAL. After eight seconds, the unit will either return a value of Go to indicate success or Err to indicate a failed calibration. You must press Mode to exit the automatic calibrate mode.
- Calibration should be performed over a bucket of water in dry areas. The gain calibration is performed when the sensor is clean and dry and exposed to only air. In cases where the relative humidity is not 100%, the sensor should be suspended in air over a source of water for best results.
- During the cleaning portion, it is important to dry the sensor completely taking care of especially at the cathode and the area around it. You can use the output signal of the sensor as a test (should be close to zero).
- For those that have extremely high salinity. In these instances any attempt to use a salinity compensation function is quite futile as above a given level there is no theoretical correction for this. If you have different values input for your salinity compensation and you have other slight errors in your calibration process you are inviting exponential theoretical corrections to occur. At this point, to get some agreement in your measurement we recommend turning salinity compensation off. This way you will have a standardised process variable amongst the various units. For any troubleshooting scenario, we suggest turning this compensation value off.
