Campbell Scientific CR3000 CR3000 Micrologger - Page 159

Section 7. Installation "offset" = "y‐ intercept" = "zero" "multiplier" = "slope" = "gain" 7.8.1.5.1 Zero or Tare (Option 0) Zero option simply adjusts a sensor's output to zero. It does not affect the multiplier. Case: A sensor measures the relative humidity (RH) of air. Multiplier is known to be stable, but sensor offset drifts and requires regular zeroing in a desiccated chamber. The following procedure zeros the RH sensor to obtain the calibration report shown. Use the integrated keyboard / display or software numeric monitor to change variable values as directed. Table 24. Calibration Report for Air RH Sensor Parameter mV output KnownRH (desiccated chamber) Argument at Deployment Argument at 30-Day Service 1000 mV 1050 mV 0 % 0 % Multiplier Offset RH reading 0.05 % / mV -50 % 0 % 0.05 % / mV -52.5 % 0 % 1. Send CRBasic example FieldCal Zeroing Demonstration Program (p. 160) to the CR3000. An excitation channel has been programmed to simulate a sensor output. 2. To place the simulated RH sensor in a simulated-calibration condition (in the field it would be placed in a desiccated chamber), place a jumper wire between channels VX1/EX1 and SE6 (3L). Set variable mV to 1000. Set variable KnownRH to 0.0. 3. To simulate a calibration, change the value in variable CalMode to 1 to start calibration. When CalMode increments to 6, zero calibration is complete. Calibrated Offset will equal -50% at this stage of this example. Figure 50: Zero (Option 0) 4. To continue this example and simulate a zero-drift condition, change variable mV to 1050. 159