VTI Instruments EX1000A, User Manual

Page: 102 / 320

VTI Instruments Corp.
102 EX10xxA Programming
The forward conversion polynomial is used to convert a CJC temperature into a compensating cold
junction voltage and has the form of:
12
12
2
2
1
1 0
* * * t c t c t c c E
     
where E is in volts, t is in ºC, and c
0
- c
12
are the coefficients.
The inverse conversion polynomial is used to convert a compensated input voltage into temperature
and has the form of:
12
12
2
2
1
1 0
* * * E d E d E d d t
     
where E is in volts, t is in ºC, and d
0
- d
12
are the coefficients.
The coefficient sets are entered with the vtex10xxA_set_user_conversion function. This function
accepts the following parameters:

an integer value of 9 or 10, corresponding to the EU conversion type (User0 or User1,
respectively) to which the entered coefficients are assigned

an array of forward conversion polynomial coefficients

an integer value corresponding to the length of the forward coefficients array

an array of inverse conversion polynomial coefficients

an integer value corresponding to the length of the inverse coefficients array
Coefficients that are not specifically defined are automatically set to 0. The current values for each
coefficient set are queried with the
vtex10xxA_get_user_conversion query.
NOTE The entry of user-defined coefficients does not automatically enable their use. The enabling is done
by setting the EU conversion to User0 or User1.
C
ONFIGURE THE
V
OLTAGE
M
EASUREMENT
C
HANNELS
The EX10xxA voltage channel can be configured to perform either general purpose voltage
measurement or thermocouple measurement. When they are used for the thermocouple
measurement, the user can use the same EU conversion functions. However, the user must use either
the user CJC temperature functionality or must connect an external thermistor to the voltage
connector (see
Voltage Connections for more information) when using temperature EUs.
To use these channels for the general purpose voltage measurement, the user must set the EU
conversion to VTEX10XXA_CONV_MV using
vtex10xxA_set_channel_conversion function.
The measurement data is returned in units of volts by default, however, custom engineering units
can be created using a linear transform specified by the
vtex10xxA_set_linear_correction function.
C
ONFIGURE THE
F
ILTER
F
REQUENCIES
The hardware filter for each channel is configured with the vtex10xxA_set_filt_freq function. A
channel’s hardware filter can be configured regardless of its inclusion in the scan list, and multiple
channels can be assigned to a specific filter frequency within one function. However, each unique
filter frequency must be set with a separate function.