Chapter 2 Configuration and Installation© National Instruments Corporation 2-19 SCXI-1120 User ManualTo determine the temperature, use the following formulas:T (°C) = T = TK - 273.15where T K is the temperature in kelvinT K = 1a + b lnR T( ) + c lnR T( )3[ ]a = 1.288 x 10-3b = 2.356 x 10 -4c = 9.556 x 10-8RT = resistance of the thermistor in ΩR T = 50,000 V TEMPOUT2.5 − V TEMPOUT V TEMPOUT = output voltage of the temperature sensorT (° F) = T (°C)[ ] 95 + 32where T (°F) and T (°C) are the temperature readings in degrees Fahrenheit and degrees Celsius,respectively.Terminal Block Jumper ConfigurationIn addition to the screw terminals, the terminal block has one jumper for configuring the onboardtemperature sensor. When you set jumper W1 on the terminal block to the MTEMP position, thejumper connects the temperature sensor to the SCXI-1120 output multiplexer. This is the factorysetting. 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-1120analog ground that is connected to MCHO- in the MTS mode, or to OUTREF or AOGND (withSCXI-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 atime. The parking position for the jumper block is the MTEMP position (the temperature sensoris 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 BlockJumper Position DescriptionW1•••• MTEMPDTEMPMTS mode selected; factorysetting; parking positionW1•••• MTEMPDTEMPDTS mode selected
