What are the critical factors affecting the choice of cables for connecting accelerometers ?

Standard industrial accelerometers are fitted with integral stainless steel over braided FEP twisted pair cable.
This cable has a twisted pair of conductors, (power/signal & common) plus a shield which provides a high level of immunity to electrical interference when installed as recommended. This makes the cable ideal for most industrial applications.

Coaxial cables are also used though they have lower immunity to interference while they may be completely adequate in some situations such as the laboratory where high power machines are not in the vicinity. These cables work well with BNC and Microdot connectors and are used in a flexible coiled assembly for connecting portable analysers to sensors switchboxes. In miniature accelerometers coaxial cables are necessary as twin core cables, though superior, are too large and heavy.

Environment
To withstand the rigours of internal and external factory and works environments with elevated temperatures, humidity, oil and other chemicals plus rain and cleaning down with high pressure hoses requires a robust cable construction. VibraSens’s standard cables use Teflon FEP insulation for high temperature resistance and chemical inertness plus overbraiding with stainless steel mesh to protect against abrasion and wear. The above cables are used up to 200ºC.

For long periods of immersion and operation down to 100m depth an external polyurethane coating with optional stainless steel overbraiding exhibits excellent water resistance and long life.

For lower temperature operation and less demanding environments like testing laboratories PVC insulated cables are acceptable and economical.

In the above examples the sensors are usually permanently mounted to machinery such that flexibility is not the most important criterion. However, for measurements with portable vibration analysers coiled, stretchable cable with PU insulation offer convenience and economy.

The performance and reliability of results from vibration sensors depends critically on their electrical connection to the measuring system. Connectors and cables must be selected carefully to ensure optimum data collection, minimum signal interference and suitability for the working environment. Cables may be directly connected to the sensor or via a plug-in connector.

Factory environments demand cabling with high levels of noise rejection, protection from external electrical fields and radiofrequency interference. Where possible, cables will be twin-core shielded. The twin cores will be twisted together and carry the power/signal and return signals. However, where cable dimensions are too large to allow connection to small and miniature sensors then single core, screened (coaxial) cables are supplied.

Extension
Cables to constant-current and 4-20mA output sensors can be extended over long distances with no significant effect on signal quality. When connecting large numbers of sensors to a remote control room it is convenient and economic to combine the cables at a junction box and make the onward connection with multi-core cables. Each sensor needs its own pair while a common shield is acceptable.

Charge output sensors, however, have very low level signals and 10m should be regarded as a normal maximum length. Following charge amplification, though, extension may proceed as above.