VTI Instruments EX1629, Руководство пользователя

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EX1629 Command Set 205
vtex1629_measure_lead_wire_resistance
F
UNCTION
P
ROTOTYPE
ViStatus vtex1629_measure_lead_wire_resistance (ViSession vi , ViInt32 channelsArraySize , ViInt32 _VI_FAR
channels[] ,ViReal64 _VI_FAR resistance[] ,ViInt32 sampleCount , ViInt32 setEuconv );
F
UNCTION
P
ARAMETERS
vi = contains a session handle to the instrument. This handle is obtained by the function and remains valid until the
session is closed.
channelsArraySize = the size of the channel[] array. Valid input values: VTEX1629_MIN_SCANLIST_LENGTH
(1) to VTEX1629_MAX_SCANLIST_LENGTH (48).
channel[] = an integer input array that specifies the channel for which the configuration will be returned. Valid input
values: 0 to 47.
resistance[] = a real return array of the measured values.
sampleCount = an integer input value indicating the number of confidence values to average.
setEuconv = a Boolean input value indicating whether or not the measured values should be used for future EU
conversions. Valid input values: VI_TRUE or VI_FALSE. See Description below for more details.
D
ATA
I
TEM
R
ESET
V
ALUE
Not applicable to this function.
D
ESCRIPTION
This function measures the lead wire resistance that exists in a strain gage set up. Specifically, there are confidence
inputs that represent the absolute voltage of the -Sense node (-BUFFERED_IN) and the -Excitation node
(-EXCITEOUT_BUFF). In a three-wire quarter bridge configuration, these points represent both sides of the lead
wire resistance that exists between the gage and the -Excitation front panel connection. Moreover, the EX1629 has
the capability, again through the confidence system, to determine the current that is flowing through the lead wire
resistance. Having the voltage drop and the current flow, the lead wire resistance is then a simple calculation.
It should be noted that there is an implicit assumption that the two lead wire resistances connecting the strain gage to
the EX1629 are essentially equal. That is, while this process measures the lead resistance that exists between the
gage and the -Excitation front panel connection, it is actually the lead resistance that exists between the gage and the
+Excitation front panel connection that causes the desensitization error. However, given that the lead wires should
be made from the same material and inherently be equal in length, this is a valid assumption.
NOTE Early EX1629s do not have hardware which supports this functionality. Implementation of direct
lead wire measurement is not possible on first generation units.
For the setEuconv parameter, a value of VI_TRUE (1) instructs the EX1629 to use the measured values for future
EU conversions. If set to VI_FALSE (0), the values are stored in the resistance[] array, but are not used in
measurements. In order for these values to be used, the user must read the array and then manually enter the values
using the vtex1629_set_lead_wire_resistance function.
E
XAMPLE
ViSession instrumentHandle;
ViStatus status = VI_SUCCESS;
ViInt32 numberOfChannels = MAX_NUMBER_OF_CHANNELS;
ViInt32 channels[MAX_NUMBER_OF_CHANNELS];
ViReal64 resistance[MAX_NUMBER_OF_CHANNELS];
ViInt32 sampleCount = 100;
int i = 0;
for(i = 0; i < numberOfChannels; i++) {
channels[i] = i;
}