NI EPM high-performance DAQ cable

NI SHC68-68-EPM Enhanced Performance Cable: The cornerstone of signal integrity for data acquisition systems

In modern data acquisition (DAQ) systems, cables are often overlooked but crucial links. A poorly designed cable may introduce crosstalk, electromagnetic interference, and grounding loops, thereby drowning valuable measurement signals. National Instruments has developed a series of specialized shielded cables for its high-performance DAQ devices, among which SHC68-68-EPM (Extended Performance Meter) has become the preferred solution for connecting M-series, DAQCard, and some S-series DAQ devices to 68 pin accessories due to its excellent noise suppression capability and signal integrity design. This article will provide a comprehensive and in-depth technical analysis of SHC68-68-EPM from the aspects of cable design concept, internal structure, technical specifications, compatibility of accessories, and selection suggestions.

Overview of NI Cable Design Advantages

National Instruments provides a variety of high-performance shielded cables for different series of DAQ devices, each designed specifically to enhance signal integrity. SHC68-68-EPM, as one of the enhanced performance models, integrates the following core technologies:

Single shielded twisted pair for analog input: Each pair of analog input signal lines is made of 30 AWG conductor and wrapped with an independent aluminum foil shielding layer. It is also equipped with drain wire for grounding connection, minimizing inter channel crosstalk and external electric field interference.

Analog output independent twisted pair: Each analog output channel also uses an independent twisted pair to avoid coupling the output signal to the input end.

The digital cables are individually wrapped and twisted with the ground wire: The digital signal cables are individually wrapped and shielded, and twisted with the ground wire to prevent high-speed digital switch noise from coupling to the analog part.

Partition bundling of analog and digital parts: The analog signal line and digital signal line are separated and bundled inside the cable to form two independent areas, further reducing the interference of digital noise on the analog circuit.

+The 5V power cord uses a 26 AWG large wire diameter conductor: providing sufficient power transmission capacity for DAQ devices and reducing voltage drop.

Integrated tin clad copper braided shielding: On top of the internal shielding layers, an additional layer of high coverage tin clad copper braided mesh is added to provide overall electromagnetic shielding and effectively suppress common mode interference.

XPbT outer sheath: made of lead-free thermoplastic elastomer material, wear-resistant, oil resistant, flame retardant, suitable for industrial environments.

These designs collectively contribute to the outstanding performance of SHC68-68-EPM in high-frequency and high-precision measurement applications.

Overview of SHC68-68-EPM Cable

SHC68-68-EPM is a high-performance shielded 68 core cable, with two end connectors:

One end: VHDCI (Very High Density Cable Interconnect) 68 pin male connector, used to connect the 68 pin I/O interface of M-series, DAQCard, or specific S-series DAQ devices.

On the other end: a 0.050-inch D-type 68 pin female connector, used to connect standard 68 pin accessories such as SCB-68 shielded junction box, SCC-68 signal conditioning carrier board, BNC-2110 BNC junction box, etc.

Available length (listed in the document):

0.5 meters (part number 192061-01R5)

1 meter (192061-01)

2 meters (192061-02)

5 meters (192061-05)

10 meters (192061-10)

Users can choose the appropriate length based on the system layout to balance signal attenuation and wiring flexibility.

Detailed explanation of internal structural technology

The internal structure of SHC68-68-EPM (see Figure 1 in the document) reflects a precise noise control strategy. Analyze layer by layer as follows:

1. Simulate input line pairs

Each analog input channel uses a pair of 30 AWG twisted wires.

Each pair of wires is covered with an independent aluminum foil shielding layer and equipped with a drain wire, making it easy for users to connect the shielding layer to the ground of the equipment or chassis.

This "individually shielded twisted pair" structure can effectively eliminate capacitive coupling and electric field crosstalk between channels, especially suitable for the transmission of low-level signals such as thermocouples and strain gauges.

2. Simulate triggering and external grounding reference line

Similarly, 30 AWG individually shielded twisted pair cables are used to ensure the purity of the triggering signal and avoid false triggering.

3. Simulate output line pairs

Each analog output channel uses independent twisted pair cables and also has separate shielding. This prevents high current transitions in the output driver stage from affecting adjacent input channels.

4. Digital signal line

Each digital signal line is twisted with a ground wire and wrapped as a whole for shielding. Digital signals usually have steep edges and radiate a large amount of high-frequency energy. By individually wrapping and twisting, the radiated noise can be limited to the interior of the line pair.