Campbell Scientific CR6 CR6 Measurement and Control System - Page 215

Section 7. Installation CRBasic Example 38. FieldCal() Zero ' the use of FieldCal() in calculating and applying a zero 'calibration. A zero calibration measures the signal magnitude of a sensor in a known zero 'condition and calculates the negative magnitude to use as an offset in subsequent 'measurements. It does not affect the multiplier. ' 'This program demonstrates the zero calibration with the following procedure: ' -- Simulate a signal from a relative-humidity sensor. ' -- Measure the 'sensor' signal. ' -- Calculate and apply a zero calibration. 'You can set up the simulation by loading this program into the CR6 and interconnecting 'the following terminals with a jumper wire to simulate the relative-humidity sensor signal 'as follows: ' U11 --- U1 'For the simulation, the initial 'sensor' signal is set automatically. Start the zero routine 'by setting variable CalMode = 1. When CalMode = 6 (will occur automatically after 10 'measurements), the routine is complete. Note the new value in variable RHOffset. Now 'enter the following millivolt value as the simulated sensor signal and note how the new 'offset is added to the measurement: ' SimulatedRHSignal = 1000 'NOTE: This program places a .cal file on the CPU: drive of the CR6. The .cal file must 'be erased to reset the demonstration. 'DECLARE SIMULATED SIGNAL VARIABLE AND SET INITIAL MILLIVOLT SIGNAL MAGNITUDE Public SimulatedRHSignal = 100 'DECLARE CALIBRATION STANDARD VARIABLE AND SET PERCENT RH MAGNITUDE Public KnownRH = 0 'DECLARE MEASUREMENT RESULT VARIABLE. Public RH 'DECLARE OFFSET RESULT VARIABLE Public RHOffset 'DECLARE VARIABLE FOR FieldCal() CONTROL Public CalMode 'DECLARE DATA TABLE FOR RETRIEVABLE CALIBRATION RESULTS DataTable(CalHist,NewFieldCal,200) SampleFieldCal EndTable BeginProg 'LOAD CALIBRATION CONSTANTS FROM FILE CPU:CALHIST.CAL 'Effective after the zero calibration procedure (when variable CalMode = 6) LoadFieldCal(true) 215