National Instruments SCXI: Part 6

Welcome to part 6 in our ongoing series about the National Instruments SCXI platform! This blog post will describe several different SCXI terminal blocks.

National Instruments has a variety of connectivity options for SCXI, including front-end terminal blocks, rack-mount terminal blocks, and DIN-rail mountable terminal blocks. Each terminal block is equipped with special features, giving you more versatility in your system. First, we will discuss some of the front mounting SCXI terminal blocks.

One of these terminal blocks is the SCXI-1300, which can be utilized to connect input signals to the SCXI-1100, SCXI-1102 Series, and SCXI-1104 modules. The SCXI-1300 is a general-purpose terminal block with an onboard temperature sensor for cold-junction compensation. You can also use the SCXI-1300 with the SCXI-1181 and SCXI-1181K modules. The SCXI-1301 is a terminal block with 20 screw terminals for use with the SCXI-1140, SCXI-1181, and SCXI-1181K modules. The SCXI-1302 has 50 screw terminals for use with the SCXI-1180 feedthrough panel.



The SCXI-1303 is a terminal block for use with the SCXI-1100, SCXI-1102, and SCXI-1102B/C modules. Designed especially for extremely precise thermocouple measurements, this terminal block has an isothermal construction that reduces errors caused by thermal gradients between terminals and the cold-junction sensor. The SCXI-1303 also includes circuitry for open-thermocouple detection, along with automatic ground referencing for floating (nongrounded) thermo-couples. When utilized with the SCXI-1102 or the SCXI-1102B/C, the SCXI-1303 delivers a high-impedance path (10 M Ohm) from the negative input terminal to ground, so the system works dependably with either floating or grounded thermocouples. When utilizing the SCXI-1100, you can configure the channels of the SCXI-1303 for floating or ground-referenced sources in blocks of eight channels.



The SCXI-1304 is designed for the SCXI-1140, SCXI-1141, SCXI-1142, and SCXI-1143 modules. The NI SCXI-1304 includes AC coupling circuitry, selectable with switches on every channel. Each channel of the SCXI-1304 additionally includes a switchable connection to ground via a 100 k Ohm bias resistor to provide a reference for floating input sources. The AC coupling circuitry on every channel has a corner frequency of 0.16 Hz, rejection capacity of +/-50 VDC, and an input impedance of 2 M Ohm differential, 1 M Ohm common mode.



The SCXI-1305 has BNC connectors for use with the SCXI-1120, SCXI-1120D, SCXI-1121, SCXI-1125, SCXI-1126, SCXI-1140, SCXI-1141, SCXI-1142, and SCXI-1143 modules. Functionally equivalent to the SCXI-1304 terminal block, the SCXI-1305 also has switchable AC coupling circuitry and ground referencing on each channel.

Another option to choose from is the SCXI-1308, which is a current input terminal block for the SCXI-1100 and SCXI-1102 Series analog input modules. Each input includes a 249 Ohms precision resistor, so you can read 0-20 mA and 4-20 mA current inputs.

However, the SCXI-1310 and SCXI-1330 connector and shell assemblies are more affordable options to SCXI terminal blocks. A connector and shell assembly are comprised of a hardened plastic enclosure and solder pins for signal connection.

With the SCXI-1313, you can extend the input range of the SCXI-1125 to 300 Vrms or 300 VDC. The extended input voltage range is enabled or disabled on a per-channel basis programmatically through software commands. The SCXI-1313 additionally has an onboard temperature sensor for cold junction compensation with thermocouples.

There is also the SCXI-1314, which is a front-mounting terminal block for the SCXI-1520 universal strain gauge input module, which can be utilized with 350 Ohm quarter bridge strain gauges. This terminal block includes a factory-installed and socketed 350 Ohm quarter-bridge completion resistor for every channel. Eight 120 Ohm resistors are included, but not installed for use with 120 Ohm quarter-bridge strain gauges. Additionally, the terminal block includes two factory-installed and socketed 100 Ohm shunt calibration resistors. All socketed resistors can be replaced by user-defined one-quarter resistors through a hole. This 8-channel terminal block offers 11 terminals for each strain gauge channel, comprised of signal +, signal -, power +, power -, remote sense +, remote sense -, quarter-bridge for each channel, two for shunt calibration A and two for shunt calibration B.



Yet another choice of terminal block is the National Instruments SCXI-1314T. This terminal block is front-mounting and created for use with the NI SCXI-1520 universal strain gage input module. The NI SCXI-1314T includes a built-in transducer electronic data sheet (TEDS) reader for Class II bridge-based smart TEDS sensors, a socketed 100 Ω shunt calibration resistor for each channel, and an RJ50 Ethernet-style connector for each channel. The 8-channel terminal block delivers 10 terminals for each channel, comprised of signal+, signal-, power+, power-, remote sense+, remote sense-, shunt cal+, shunt cal-, TEDS+, and TEDS-.

The last front-mounting terminal block to be discussed today is the National Instruments SCXI-1315. This one is an 8-channel, front-mounting terminal block for the NI SCXI-1540 LVDT input module with six terminals for each LVDT channel — CH+, CH-, EX+, EX-, Synch, and GND. With the SCXI-1315, you achieve a convenient connection to linear variable differential transformers (LVDTs), rotary variable differential transformers (RVDTs), and resolvers via screw terminals. There are 48 terminals organized in eight groups of six. Each group corresponds to one of the eight channels available on the NI SCXI-1540.



Next week, part 7 in our SCXI blog series will discuss other types of front mounting SCXI terminal blocks. Keep checking back for future posts!