Example 10: corr_metsmeth - Temperature correction of METS methane output

An RBRconcerto C.T.D.METS has a METS methane sensor from Franatech in addition to the usual C, T and D channels. The METS sensor also has its own temperature output, used to compensate the temperature dependence of the raw methane output, and to monitor this requires a fifth channel in the logger, Tm. See the section corr_metstemp - Temperature measured by a METS (methane sensor) for details of this temperature channel.

The equation for the temperature corrected concentration output of the methane sensor, Cm, as provided by Franatech, is as follows:

Cm = exp[ c0*ln{ (c1 + c2*exp(-Vt/c3)) * (1/Vm - 1/(c4 + c5*exp(-Vt/c6))) } ]

where

• c0...c6 are coefficient values provided by Franatech,
• Vm is the voltage in Volts from the sensor's methane output,
• Vt is the voltage in Volts from the sensor's temperature output.

Franatech's calibration documentation may have no formal naming convention for the coefficients, in which case the values will be simply shown in an equation on the calibration sheet. The terms c0...c6 are those used by the logger's calibration command to report or set the values: if updating, be careful to assign the correct values to each coefficient.

 The sensor output voltage for methane concentration, Vm, is related to the logger's reported voltage ratio R by a simple linear equation, the coefficients of which (x0,x1) are determined by RBR Ltd at the factory.

The sensor output voltage for temperature, Vt, is an intermediate variable in the calculation of temperature from the supporting channel, and can be back-calculated from that result:

where

•  ct0, ct1 are the primary coefficient values for the supporting temperature channel,
• Tm is the temperature output of that channel in °C, value(n0). 

Example commands:

( Confirm the channel type )

( Set the coefficients provided by Franatech )

( Set the secondary coefficients for the voltage conversion )

( Request confirmation of everything for primary methane channel )

( Confirm main coefficients of temperature compensation channel )