QuickTip: Transducer Cable Management

Although wireless technology is enabling some remote sensing applications within the facilities monitoring and equipment health markets, most critical testing and monitoring application transducers require high-performance cable to connect them to the signal conditioning / data acquisition system. For most tests, those cables must be carefully managed to assure the most reliable and accurate data gathering and that is the topic of this Endevco QuickTip.

Q. Why Cable Management?
A. The Triboelectric Effect

Cables that transport signals from Piezoelectric devices to charge amplifiers have special requirements that differ from Integral Electronics/Piezoelectronic (Isotron®), Piezoresistive and Variable Capacitance (Microtron®) devices. Since charge converters such as Endevco's 2777 are required to convert the multiplicand of capacitance and voltage from PE devices the cable becomes a critical factor in measurement success. The change in distance between the cable's center conductor and shield as the cable flexes, can be seen as a change in charge (capacitance) as if being generated by the transducer itself. This charge is seen by the charge converter as signal, and is indistinguishable from the vibration signal of interest. This is the known as the Triboelectric effect. Endevco cables for PE transducers are tested inch for inch, using a charge converter, to make sure it complies with our low noise specification. But even the world's lowest noise cable needs to be properly managed to provide the most reliable and accurate measurement results.

Cable Management

As a minimum precaution, all cables connecting transducers to signal conditioning equipment need to be tied down to prevent cable whip from separating the cable from the device. For example, a cable that weighs 16 ounces will weigh an equivalent of 100 pounds when subjected to a 100g shock! Cables should be tied down, in general, every inch, starting 1/2 to 1 inch from the transducer, to the point where the cable leaves the area of vibration or shock. As seen in the example above, this is more critical at higher g levels than at 50g and less. This will also reduce any Triboelectric effects and provide the most reliable data.

Proper grounding techniques, while outside the scope of this QuickTip, are vital, and can be a cable management consideration at the level of proper selection of cable to use for a particular test. For those situations where there is a likelihood of radio frequency signals interfering with the vibration data, differential piezoelectric (ex:6233) and Piezoresistive (ex: 7264B) devices and their associated cables (Endevco 6960 and 3022B, respectively) are available from Endevco. In some extreme situations, differential piezoelectric and double-shielded cable is necessary, and is also available (Endevco 6961/6963).

Proper cable selection, routing and tie-down are critical to achieving the most reliable and accurate results for vibration monitoring. We hope this QuickTip was helpful but if you have any questions on this, or other subjects, please call Endevco Applications Engineering or Customer Service.


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