Configuration and Installation Chapter 2SCXI-1120 User Manual 2-18 © National Instruments CorporationThe following warnings contain important safety information concerning hazardous voltages andterminal blocks.Warnings: When using the terminal block with high common-mode voltages, you mustinsulate your signal wires appropriately. National Instruments is not liable for anydamages or injuries resulting from inadequate signal wire insulation.If high voltages (≥42 Vrms) are present, you must connect the safety earth groundto the strain-relief tab. This complies with UL 1244 and protects against electricshock when the terminal block is not connected to the chassis. To connect thesafety earth ground to the strain-relief tab, run an earth ground wire in the cablefrom the signal source to the terminal block. National Instruments is not liable forany damages or injuries resulting from inadequate safety earth groundconnections.When connecting your signals to the SCXI-1320 terminal block for use with the SCXI-1120,follow the labeling on the SCXI-1320 indicated under the module type column for theSCXI-1120 as indicated in Figure 2-9.When connecting your signals to the SCXI-1328 high-accuracy isothermal terminal block for usewith the SCXI-1120, follow the labeling on the SCXI-1328 indicated along the module type rowfor the SCXI-1120 as indicated in Figure 2-10.Terminal Block Temperature SensorTo accommodate thermocouples with the SCXI-1120, the terminal block has a temperaturesensor for cold-junction compensation. You can connect the temperature sensor in two ways:• You can connect the temperature sensor to the MTEMP pin (C4) on the module frontconnector and multiplex the sensor at the output multiplexer along with amplifier outputs.This is the Multiplexed Temperature Sensor (MTS) mode. Refer to the ConfigurationRegister section in Chapter 4, Register Descriptions, for further details.• You can connect the temperature sensor to a separate data acquisition channel via pin 18 onthe module rear signal connector when you set SCXI-1120 jumper W41 to position 3. This isthe Direct Temperature Sensor (DTS) mode.Note: Use an average of a large number of samples to obtain the most accurate reading.Noisy environments require more samples for greater accuracy.The SCXI-1320 temperature sensor outputs 10 mV/°C and has an accuracy of ±1° C over the0° to 55° C temperature range. To determine the temperature, use the following formulas:T (°C) = 100(V TEMPOUT )T (° F) = T (°C)[ ] 95 + 32where V TEMPOUT is the temperature sensor output and T (°F) and T (°C) are the temperaturereadings in degrees Fahrenheit and degrees Celsius, respectively.The SCXI-1328 temperature sensor outputs 0.62 to 0.07 V from 0° to 55° C and has an accuracyof ±0.35° C over the 15° to 35° C range and ±0.65° C over the 0° to 15° and 35° to 55° C ranges.
