Campbell Scientific CR5000 Measurement and Control Module - Manual (Page 61)

Section 3. CR5000 Measurement Details
3-7
measurements are repeated on the same channel the settling time is only
necessary before the first measurement (as long as the excitation polarity and
differential inputs are not reversed).
Before the program to measure the settling time is run, the sensor with the
cable that will be used in the installation needs to be connected and the sensor
needs to be stabilized. If the sensed value is changing rapidly it will be
difficult to separate the settling time from true changes in the value measured.
The following program measures the settling time on a full bridge pressure
transducer.
'CR5000
'Program to measure the settling time on a Pressure Transducer
'Declare the variable array for the 20 Pressure Transducer measurements:
public PT(20)
'Set up the output table for the measurement data:
DataTable (SetlDat,1,5)
Sample (20,PT(),IEEE4)
EndTable
'The following program repeats the 20 measurements 5 times:
BeginProg
Scan (1,Sec,3,5)
'The -1 in the differential channel parameter of BrFull tells
'the CR5000 to make the 20 measurements on channel 1:
BrFull (PT(),20,mV50,-1,Vx1,20,5000,False,False,0,0,1.0,0)
CallTable SetlDat
NextScan
EndProg
The program was run on a Druck water level pressure transducer with 200 feet
of cable. The first six measurements of each of the 5 readings are shown in
Table 3.3-1. The reading has settled by the second measurement, PT(2), thus a
settling time of 200
µ
s is adequate.
Table 3.3-1. First Six Values of Settling Time Data
PT(1) PT(2) PT(3) PT(4) PT(5) PT(6)
0.291257 0.052925 0.053937 0.054274 0.057645 0.056296
0.292269 0.052925 0.053262 0.054948 0.055622 0.056633
0.286538 0.053937 0.054274 0.055959 0.053599 0.054948
0.284515 0.052925 0.052925 0.053599 0.057645 0.055285
0.286875 0.052925 0.052925 0.054611 0.056296 0.057308
3.4 Thermocouple Measurements
A thermocouple consists of two wires, each of a different metal or alloy, which
are joined together at each end. If the two junctions are at different
temperatures, a voltage proportional to the difference in temperatures is
induced in the wires. If the junctions are at the same temperature, there is no
voltage. When a thermocouple is used for temperature measurement, the wires
are soldered or welded together at the measuring junction. The second