Chapter 8 Tutorial

Low-Level Signal Multiplexing and Switching

Sources of Error in Multiplexing and Switching

Noise can be coupled inside a switch by the drive circuitry, by switch thermal EMFs, or by coupling among signal paths. Noise can also be generated outside the network and conducted or coupled into the switch. Although noise problems apply to the entire system, they can become especially acute for switching. Switch networks contain a high concentration of signals, which magnify the errors. Most problems with electric noise can be traced to improper grounding and shielding (for more information on grounding and shielding, see page 337).

Noise can be capacitively coupled between physically adjacent channels in a switching system. Noise can be coupled between the switch contacts themselves (Csw) or between adjacent cabling (Cadj).

Cadj

Source

Source

CswSource

Source

DMM

Capacitive noise coupling is a function of area and proximity. A simple method to reduce the noise coupling is to physically separate the switches and cables from each other. However, this may not be practical for all applications.

Another solution is to keep large amplitude signals and small amplitude signals away from each other. Group similar signals together (high voltages, low voltages, analog, and digital). If possible, use two separate switch modules; one for high-level signals and one for low-level signals. If you are using a single module for mixed-signal switching, leave one unused, grounded channel between the groups. Also, ground any unused channels on the module.

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Agilent Technologies 34970A manual Sources of Error in Multiplexing and Switching
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34970A specifications

Agilent Technologies 34970A is a versatile data acquisition and measurement system that has gained popularity in various industries, including research and development, manufacturing, and education. The primary purpose of the 34970A is to offer an efficient solution for data collection, monitoring, and analysis, which can significantly enhance productivity and accuracy in testing applications.

One of the main features of the 34970A is its modular design, allowing users to customize the system according to their specific measurement needs. The mainframe can accommodate up to three plug-in measurement modules, which can include various types of measurements such as analog, digital, temperature, and frequency. This modularity provides flexibility for users to tailor the system to their requirements, making it highly adaptable to different applications.

Another notable characteristic of the Agilent 34970A is its impressive channel configuration. The system can support up to 120 measurement channels when fully configured, enabling extensive data acquisition without the need for multiple devices. This capability is essential for applications requiring simultaneous monitoring of multiple parameters or locations.

The 34970A utilizes advanced signal processing technologies to ensure high-accuracy measurements. The internal 6.5-digit resolution multimeter provides precise readings, while the device also supports various input types, such as thermocouples and RTDs for temperature measurements. The ability to perform mathematical functions, such as summation and averaging, on the acquired data further enhances its usability.

For data storage and management, the Agilent 34970A features built-in memory for storing up to 20,000 readings. Users can also easily transfer data to a PC through the RS-232 interface or GPIB (IEEE 488) for further analysis and reporting. Additionally, it offers the capability to program automatic data logging and scheduling of measurements, which streamlines the testing process and reduces manual intervention.

In terms of user interface, the 34970A is equipped with a large graphical display that provides clear visualization of measurement data and easy navigation through settings and options. The menu-driven interface makes it accessible for users of all skill levels, simplifying the setup and operation of the device.

Overall, the Agilent Technologies 34970A stands out for its modularity, high channel capacity, advanced measurement technologies, and user-friendly interface. As a reliable and efficient data acquisition system, it is well-suited for a wide range of applications, making it an essential tool for engineers and technicians looking to enhance measurement precision and efficiency.
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