What are the best practices for cleaning transducers and cables?
I am concerned that my "less than clean" lab environment may be contaminating some of my devices and introducing unwanted noise in my measurement system.
This is a great question and one deserving of a detailed answer. Vibration monitoring transducers require intimate contact with the vibration producing device. Pressure transducers require a tight seal to the device to be measured. The electrical connections must have no contamination, or signal loss is possible (usually at the worst possible moment!)
Accelerometers can be mounted with a threaded device-screw or bolt, or adhesively. For screw or bolt mounted devices, the mounting surface must be very flat, with low roughness, and must be perpendicular to the threaded hole(s) used to mount the accelerometer. If there was adhesive used on any of the surfaces before a thorough cleaning is absolutely necessary to remove all traces of the adhesive. Any aberrations on the mounting surface will cause base strain causing errors in the reading. For adhesively mounted accelerometers the cleanliness extends to the complete accelerometer. If there is adhesive left on the base, there will be a base-to-device coupling problem. If there is glue elsewhere, the characteristics of the transducer's sides and top could change and result in additional crosstalk.
For the to-be-measured device on new installations, cleaning compounds are left to the user, except that the surface after cleaning must be free of contaminants, and dry. For Endevco accelerometers, the cleaner depends on the transducer and the contamination. If the transducer's base is visibly scratched, the cleaning will include a flat plate and wet 600 grit emery cloth. For cyanoacrylate (zip-grip, superglue, Loctite®, etc) adhesive mounts, Acetone is the recommended solvent, although Loctite® provides X-NMS Clean up Solvent, which also works very well. Both Acetone and X-NMS are capable of harming certain non-hermetic transducers, so careful wetting and sparse use of these aggressive solvents is advised.
For pressure transducers, the surface preparation is the same (surface flatness, perpendicularity of the tapped pressure sensing hole, and cleanliness of the surfaces). There should not be any issues with adhesives, since there is, in most installations, no value to the addition of adhesive to the mounting methods.
In addition to careful preparation of the transducer and mounting surface users must also attend to the cable and connections to assure the lowest noise integration. Primarily when dealing with Piezoelectric (PE) transducers, care must be taken to guarantee no contamination of the transducer or cable connection. The characteristic impedance of PE transducers is 10^12 Ω. With impedances that high, even moisture can cause signal degradation. Cleaning with alcohol and a clean, new, lint free wipe is recommended every time a connector is to be mated, just before mating. This is not as critical with Isotron® and Piezoresistive devices, though a sliver of conducting material can get in the device's connector, and this would cause a short circuit or non-operation of the transducer due to current draw. It follows that the connector at the signal conditioner is just as susceptible to contamination, and these practices should be followed there as well.
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