I. Product Introduction

NI SCB-68 is a 68-pin shielded desktop I/O junction box launched by National Instruments. It is used to convert the high-density connectors of NI 68-pin interface data acquisition devices and digital I/O modules into 68 screw terminals, facilitating on-site signal wiring and debugging. The body is equipped with a full shielding structure and an internal cold junction compensation sensor. It also integrates two universal breadboards, supporting the construction of custom circuits and can be adapted to various signals such as analog, digital, and thermocouples. It is a commonly used front-end adapter for industrial testing and laboratory data acquisition.

II. Model Interpretation

SCB represents the shielded junction box series identifier, and 68 indicates that the device is equipped with 68-pin standard interfaces and corresponding 68 terminals. This product has an official component number, the general version number is 776844-01, and the high-speed digital-specific version number is 782914-01. The upgraded model of the same series is SCB-68A, with fully compatible hardware functions and only an optimized structure layout.

III. Technical Parameters

The device host end uses 68-pin SCSI-type connectors, which can be used with the same specification shielded cables. The output end is 68 screw terminals, suitable for wire gauge ranges of 30 to 12AWG, with a standard tightening torque of 0.5 Newton-meters for the screw terminals. The built-in cold junction compensation temperature sensor has a measurement accuracy of ±0.5 degrees Celsius and supports open-circuit fault detection for thermocouples. The body integrates two universal breadboards, allowing for the self-welding of electronic components to build simple conditioning circuits. The device is powered by a DC 5-volt supply from the data acquisition module, with a 800-milliamp fuse onboard for circuit protection, and the typical power consumption of the entire unit is 10 milliamperes. The signal circuit has a maximum tolerance of 30 volts AC and 60 volts DC, only for low-voltage signal scenarios. The operating temperature range is 0 degrees Celsius to 55 degrees Celsius, the storage temperature range is from -55 degrees Celsius to 125 degrees Celsius, the working environment humidity is 5% to 90%, and there is no condensation. The product complies with RoHS environmental requirements. The entire unit is of a desktop structure, weighing approximately 500 grams.

IV. Interfaces and Communication Configuration

One side of the device is a 68-pin connector, connected to data acquisition cards, digital I/O modules, counter modules, etc., through matching shielded cables. All screw terminals are arranged on the front, allowing for direct connection to sensors, thermocouples, relays, and various external signal lines. The body is equipped with a DIP switch, which can switch between direct connection, thermocouple, current input, and other working modes. The breadboard area is reserved for soldering pads, allowing for the expansion of custom circuits for filtering, voltage division, signal conversion, etc. The device is a pure hardware adapter, requiring no installation of drivers, relying on the shielding shell and shielded cables to reduce external electromagnetic interference and ensure stable signal transmission.

V. Core Functions

It completes the interface form conversion, converting high-density connectors into conventional screw terminals, simplifying on-site wiring, line maintenance, and equipment debugging. The all-metal shielding structure can effectively resist electromagnetic interference and improve the transmission quality of weak signals. The built-in cold junction compensation unit automatically completes temperature compensation when using thermocouples for temperature measurement, and also has open-circuit detection capabilities, effectively reducing measurement errors. The integrated breadboard allows for the autonomous construction of signal conditioning circuits, achieving filtering, level conversion, current-voltage conversion, and other functions, suitable for various signal requirements. The working mode can be flexibly switched by the DIP switch, compatible with analog acquisition, digital input/output, high-speed digital signals, timing counting, and other application scenarios. The onboard fuse and cable fixation structure provide circuit protection for the downstream equipment and avoid cable detachment, improving overall usage reliability.

VI. Application Scenarios Applied in the field of industrial automation, it realizes the conversion of digital and analog signals of equipment such as production line sensors, relays, and actuators. Combined with the full range of NI data acquisition cards, it can complete the data acquisition of multiple voltage, current, and temperature signals. It can be adapted to high-speed digital input/output modules, used for high-speed signal conversion in semiconductor testing and automated testing equipment. It is suitable for various laboratory research and teaching scenarios. Relying on the onboard breadboard, it can quickly build and verify custom signal conditioning circuits. It can also be applied to small temperature control systems, cooperating with thermocouples to complete multi-point temperature monitoring of heating equipment and environmental enclosures. Instruction Manual

Before conducting wiring operations, make sure to disconnect the power supply of the data acquisition module from the junction box. Connect the shielded cables to the 68-pin interfaces of the equipment and the junction box respectively, and fasten the fixing clips. According to the specifications, remove the insulation layer of the wires and connect them to the corresponding terminals. Tighten the screws with the standard torque to prevent false connections or damage to the wire cores due to compression. Adjust the jumpers according to the actual usage requirements, select the corresponding positions for analog signals and thermocouple measurements, and set the high-speed digital module to the bypass mode when using it. When soldering components on the breadboard, strictly check the circuit to avoid short circuits, and connect the current signal with a sampling resistor. Connect the thermocouple directly to the designated terminal. Before powering on, thoroughly inspect the circuit connections, cable appearance, and fuse status. Do not connect to high-voltage power supply lines and ensure that the circuit voltage does not exceed the rated range.

Maintenance Instructions

During daily use, wipe the surface of the equipment and the terminal blocks with a dry soft cloth. Clean up the accumulated dust promptly to avoid placing and using the equipment in a humid environment. Regularly check the terminal blocks, connectors, and associated cables to check for any looseness, oxidation, or damaged outer sheaths. Address any faults promptly. When a 5-volt DC circuit shorts, first cut off the power supply to troubleshoot the cause, and then replace the fuse of the same specification. The working area of the equipment should be kept ventilated and dry, away from strong electromagnetic radiation sources, high-temperature heat sources, and corrosive gases. When the equipment is not in use for a long time, disconnect all external connections, place the equipment in a cool and dry environment for storage. Do not plug in or unplug interface cables or turn the terminal block screws while the equipment is powered on, to avoid abnormal signals or hardware damage.