National Instruments SCXI-1120 - Manual (Page 35)

Chapter 2 Configuration and Installation
© National Instruments Corporation 2-19 SCXI-1120 User Manual
To determine the temperature, use the following formulas:
T (
°
C) = T = T
K
- 273.15
where T
K
is the temperature in kelvin
T
K
=
1
a
+
b lnR
T
( )
+
c lnR
T
( )
3
[ ]
a = 1.288 x 10 -3
b = 2.356 x 10 -4
c = 9.556 x 10 -8
R
T
= resistance of the thermistor in
Ω
R
T
=
50, 000
V
TEMPOUT
2.5
−
V
TEMPOUT

 

V
TEMPOUT
= output voltage of the temperature sensor
T (
°
F)
=
T (
°
C)
[ ]
9
5
+
32
where T (
°
F) and T (
°
C) are the temperature readings in degrees Fahrenheit and degrees Celsius,
respectively.
Terminal Block Jumper Configuration
In addition to the screw terminals, the terminal block has one jumper for configuring the onboard
temperature sensor. When you set jumper W1 on the terminal block to the MTEMP position, the
jumper connects the temperature sensor to the SCXI-1120 output multiplexer. This is the factory
setting. The DTEMP position connects the temperature sensor to SCXI-1120 jumper W41.
In both MTS and DTS modes, the reference to the temperature sensor signal is the SCXI-1120
analog ground that is connected to MCHO- in the MTS mode, or to OUTREF or AOGND (with
SCXI-1120 jumper W46 set in positions AB-R2 and AB-R0, respectively) in the DTS mode.
One jumper block comprises both positions; thus, you can use only one type of configuration at a
time. The parking position for the jumper block is the MTEMP position (the temperature sensor
is disabled until the RTEMP bit in the Configuration Register selects the sensor).
Tables 2-7 and 2-8 show the jumper settings on the SCXI-1320 and SCXI-1328 terminal blocks.
Table 2-7. Jumper Settings on the SCXI-1320 Terminal Block
Jumper Position Description
W1
• •
• • MTEMP
DTEMP
MTS mode selected; factory
setting; parking position
W1
• •
• • MTEMP
DTEMP
DTS mode selected