National Instruments 777687-03 Isothermal Terminal Block 

National Instruments part number 777687-03 is an identifying part number for the SCXI-1303, an Isothermal Terminal Block with 32 Channels and 78 Screw Terminals. The National Instruments 777687-03 Terminal Block is ideal for high-precision thermocouple temperature measurement tasks. It features an exceptionally accurate thermistor cold-junction temperature sensor and an isothermal copper plane that minimizes temperature differentials across the screw terminals during thermocouple measurements. This module includes specialized capabilities like open thermocouple detection, signal ground referencing, and isothermal design, ensuring accurate and reliable temperature readings in demanding measurement applications. 

The part number 777687-03 is recommended for use with the following SCXI modules: the SCXI- 1100/1102/1102B/1102C.  This module includes pull-up and bias resistors that apply +5 V to open channels, causing them to saturate at the positive rail. It comes pre-installed with 10 Ω and 10 MΩ bias resistors. For optimal performance with SCXI-1102/B/C modules, it is recommended to use the 10 MΩ factory-installed resistors. These resistors help in maintaining proper voltage levels and ensure effective signal conditioning within the SCXI system, enhancing overall measurement accuracy and reliability. 

This Terminal Block provides 78 screw terminals for convenient signal connections. Thirty-two pairs of screw terminals are dedicated to the 32 differential inputs of the SCXI modules. One pair of terminals connects to the chassis ground pins on the module. Additionally, three terminals are used for linking to the SCXI module OUTPUT, AOREF pins, and the SCXIbus GUARD. The remaining terminals are reserved for future use. Each input channel on the terminal block includes a pullup resistor connected between CH+ and +5 V, as well as a bias resistor connected between CH– and chassis ground. These resistors are essential for detecting open thermocouples by ensuring that the module amplifier output is saturated when necessary. National Instruments has declared obsolete status for the 777687-03, however, it is still available for purchase on the Apex Waves website.