VTI Instruments EX1629 - Vtex1629_Set_Excitation

VTI Instruments Corp.
256 EX1629 Command Set
vtex1629_set_excitation
FUNCTION PROTOTYPE
ViStatus vtex1629_set_excitation (ViSession vi, ViInt32 _VI_FAR channels[], ViInt32 numberOfChannels,
ViReal64 positiveExcitationVoltage, ViReal64 negativeExcitationVoltage);
FUNCTION PARAMETERS
vi = contains a session handle to the instrument. This handle is obtained by the function and remains valid until the
session is closed.
channels = an input integer array containing a list of channel numbers for which the programmed excitation voltage
will be set. Valid input values: 0 to 47.
numberOfChannels = the size of the channels list. Valid input values: 1 to 48.
positiveExcitationVoltage = a real input value, in volts, indicating the programmed positive excitation voltage.
Valid input values: 0.000000 through 8.000000.
negativeExcitationVoltage = a real input value, in volts, indicating the programmed negative excitation voltage.
Valid input values: -8.000000 through 0.000000.
DATA ITEM RESET VALUE
positiveExcitationVoltage = 0.000000 negativeExcitationVoltage = 0.000000
DESCRIPTION
This function sets the programmed excitation voltages for a given list of channels. The excitation value is quantized
with a 14-bit DAC. Hence, the actual value can be queried with the vtex1629_get_excitation function. Additionally,
the accuracy specifications (EX1629 Specifications) for the instrument require that the excitation voltage be
measured (see vtex1629_measure_excitation_voltage) prior to taking strain gage readings.
Providing separate positive and negative excitation supply control permits the mid-point of each half of the bridge to
be at a voltage other than 0. This is achieved by using asymmetric excitation voltages (e.g., +5.0 V and -1.0 V will
produce 2.0 V at the mid-point of each half of the bridge.
NOTES 1) Due to hardware limitations, the setting of excitation voltages with a magnitude less than
100 mV may be imprecise. However, since the excitation voltage must be measured and the EU
conversion variables updated prior to taking strain measurements, per the instrument
specifications (EX1629 Specifications), this imprecision does not effect the accuracy of the
strain gage readings.
2) The control of the excitation voltage values and their enabling are separate operations. Thus,
setting a non-zero value for either parameter does not guarantee that the excitation source is
enabled. That must be set with the vtex1629_set_excitation_enabled function.
EXAMPLE
ViSession instrumentHandle;
ViStatus status;
ViInt32 channels[] = {0};
ViInt32 numberOfChannels = 1;
…
status = vtex1629_set excitation(instrumentHandle,
channels,
numberOfChannels,
2.0,
-2.0);