In practice this is perhaps an unlikely scenario, and so a rather artificial example, but it is useful to use the simple equation for pH to illustrate the concept. Consider an RBRconcerto monitoring conductivity and several electrochemical sensors, including pH. The deployment conditions are already known to have a temperature which is approximately constant, so the instrument does not monitor temperature: perhaps the instrument is on the sea bed, and so at about 4°C all the time. But this is very different from the typical calibration temperature for pH of 25°C, so it would be desirable to correct the readings.
The compensated version of the equation itself is not changed:
but now there is no temperature channel, and so no value we can use for n0. In a case like this, n0 will not have a numeric value of a logger channel index, but will be set at the factory to the special text string "value". The logger knows that a temperature value is required in the equation, and so will use the substitute temperature value "sub(T)" specified by the "settings temperature" command, instead of "value(n0)".
In this instance, the equation effectively takes the form below, and in the above example "sub(T)" might have a value such as 3.9 (in °C):
Example commands:
<< calibration 4 type = ph__02
( Confirm the channel type )
( Set the core coefficients )
( Set the cross-channel correction coefficients )
>> calibration 4
<< calibration 4 type = ph__02, datetime = 20130401120005, c0 = 15.23461,c1 = –0.198743, x0 = –0.00302, x1 = 7, x2 = 24.943, n0 = value
( Request confirmation of everything )
>> settings temperature = 3.9
<< settings temperature = 3.9
( Set the value of the substitute temperature )