VXI VT1422A - Manual (Page 85)

Programming the VT1422A & VT1529A/B for Remote Strain Measurement 83 Chapter 3
Measure Strain Using
User Specified EU
Conversion
The VT1422A measures voltage and then applies a conversion routine
(linear) supplied by the user. The user must supply the slope (M) and offset
(B) of a linear M*volt + B conversion.
The DIAGnostic:CUSTom:MXB <slope>,<offset>,(@<ch_list>)
command is used to supply the slope and offset for the strain conversion. To
select the custom linear conversion to be used, the command
SENSe:FUNCtion:CUSTom [<range>,](@<ch_list>) must be sent before
starting measurements with the INIT command.
Before taking a measurement the following must be done:
1. The type of bridge connection must be specified using the
[SENSe:]STRain:BRIDge[:TYPE] <select>,(@<ch_list>)
command. The allowable values for <select> are: FBEN, HBEN,
Q120 (quarter bridge, 120
Ω), Q350 (quarter bridge, 350 Ω) or USER
(quarter bridge, with the user supplied resistor). The power-on and
*RST default setting is FBEN.
2. Configure channels to measure their strain bridge outputs rather
than their excitation supply. This is done by sending the
[SENSe:]STRain:CONNect BRIDge,(@<ch_list>) command.
The power on and reset setting is BRIDge.
3. Turn on excitation voltage to the strain bridges with the
SENSe:STRain:EXCitation:STATe ON,(@<ch_list>) command.
4. The linear conversion slope and offset (M and B) must be input via
the DIAG:CUST:MXB command as mentioned above. The user must
supply M and B, both of which are functions of the excitation voltage,
the unstrained reference and the gage factor.
5. The VT1422A must be told to use the custom conversion when
taking measurements. This is done by sending the
SENSe:FUNC:CUSTom [<range>,](@<ch_list>) command.
Figure 3-17 shows the sequence of commands to convert remote measurements
according to the user’s own downloaded EU conversion method.