Campbell CR800 Series, Руководство оператора

Страница: 326 / 598

Section 8. Operation
326
TABLE: Offset Voltage Compensation Options
(p. 326)
lists some of the tools
available to minimize the effects of offset voltages.
Offset Voltage Compensation Options
CRBasic
Measurement
Instruction
Input Reversal
( RevDiff = True )
Excitation
Reversal
( RevEx = True )
Measure
Offset During
Measurement
( MeasOff = True )
Measure Offset
During
Background
Calibration
( RevDiff = False )
(
RevEx
=
False
)
( MeasOff = False )
AM25T()
 

BrHalf()
 
BrHalf3W()
 
BrHalf4W()
  
BrFull()
  
BrFull6W()
  
TCDiff()
 
TCSe()
 
Therm107()
 
Therm108()
 
Therm109()
 
VoltDiff()
 
VoltSe()
 
Input and Excitation Reversal
Reversing inputs (differential measurements) or reversing polarity of excitation
voltage (bridge measurements) cancels stray voltage offsets. For example, if 3
µ
V offset exists in the measurement circuitry, a 5 mV signal is measured as 5.003
mV. When the input or excitation is reversed, the second sub-measurement is –
4.997 mV. Subtracting the second sub-measurement from the first and then
dividing by 2 cancels the offset:
5.003 mV – (–4.997 mV) = 10.000 mV
10.000 mV / 2 = 5.000 mV
When the CR800 reverses differential inputs or excitation polarity, it delays the
same settling time after the reversal as it does before the first sub-measurement.
So, there are two delays per measurement when either RevDiff or RevEx is used.
If both RevDiff and RevEx are True , four sub-measurements are performed;
positive and negative excitations with the inputs one way and positive and
negative excitations with the inputs reversed. The automatic procedure then is as
follows,