How does the JBL pH-Control recognise a “bad“ sensor?
The pH sensor transmits a voltage to the measuring device, which convert the voltage into the pH value.
This voltage does NOT remain constant throughout the service life of the sensor! It needs to be calibrated regularly. The device is thus informed about the age-related change in voltage and can display reliable values again.
The calibration takes place at pH 7 and pH 4.
At pH 7 a new sensor transmits a voltage of 0 mV (+/- a few mV) to the measuring device. The more the voltage at pH 7 deviates from 0, the older the sensor is. The deviation can occur at + or -. At a deviation of more than +40 or -40 mV the device rejects the sensor.
The error message OFFSET appears.
NOTE: The same error message appears if you accidentally begin to calibrate at 4!!
At pH 4 the sensor transmits a voltage of about +186 mV (when 7 is at 0 mV). This means that between the single steps (4-5; 5-6 and 6-7) there is in each case a difference of about 62 mV. The smaller this difference, the older the sensor. With differences below 30 mV the device rejects the sensor.
The error message DELTAV appears.
NOTE: The same error message also appears, when you accidentally calibrate twice at 7!!
IMPORTANT: Rejected sensors can often be brought “back into operation” if you soak them intensively in storage solutions (for several days)!