Campbell-scientific CR9000X Measurement and Control System Manual de usuario descargar pdf (Pagina 368)

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101

Section 9. Program Control Instructions

FIGURE 9-1A. Active gage shunt FIGURE 9-1B. Resistor shunt

When using Campbell Scientific's Terminal Input Modules (TIM) with shunt

posts (e.g. model # 4WFBS350), the R2 resistor shown in Figure 9-1B:

Resistor Shunt can simply be shorted across the gold posts located on the top

of the TIM.

Campbell Scientific recommends that the user record the

calibration constants to a data table and upload them to his PC

for a record.

NOTE

When a calibration is complete, the *.CAL file will be updated, and the

NewFieldCal function state will be changed to True. The NewFieldCal

function can be used to trigger a user created Data Table to store the

calibration factors.

The values from the *.CAL file can be loaded back into the calibration

variables using the LoadFieldCal instruction.

Description of the ¼ Bridge calculations performed by the datalogger.

The premise is the same when shunting across either arm. The shunted arm

undergoes a reduction in resistance creating a simulated strain. A precision

resistor should be used for the shunt resistor. The change in resistance of the

shunted arm is given by:

−

Variable definitions:

ΔR = Change in arm resistance (ohms)

= Nominal gauge resistance (ohms)

= Shunt resistor resistance (ohms)

The standard equation for calculating micro-strain from the change in

resistance of the gauge is:

με

ΔR

Variable definitions:

με = micro-strain

ΔR = Change in arm resistance (ohms)

R = Nominal gauge resistance (ohms)

GF = Gauge factor

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Campbell-scientific CR9000X Measurement and Control System Manual de usuario Pagina 368

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