Frequency of inspection – This is quite subjective and depends upon the severity of the service and how critical the accuracy of the indicated speed is. For example, a monthly inspection frequency may be in order for critical, severe service applications. Annual inspections, or even less frequent schedules, are often employed in non-critical applications.
In-service inspection – If the accuracy of the tachometer cannot be checked in place, the user can at least look for (a) erratic or random pointer motion; (b) readings that are suspect – especially indications of speed when the user believes the true speed is 0 rpm. Any tachometer which is obviously not working or indicating erroneously should be immediately removed from service and inspected.
When to check accuracy – Any suspicious behaviour of the tachometer pointer warrants a full accuracy check be performed. Even if the tachometer is not showing any symptoms of abnormal performance, the user may want to establish a frequency of inspection.
Other considerations – These include (a) bent or unattached pointers; (b) broken windows which should be replaced to keep dirt out of the internals; (c) shaft damage/corrosion; (d) case damage – dents and/or cracks; (e) shaft bearings damage/noise.
Instrument failure – Any instrument suspected to be faulty should be returned to Fawcett.
Temperature – To ensure long life and accuracy, mechanical tachometers should preferably be used at a ambient temperature between 0° and +50°C. Extremes of temperature will cause accuracy errors with the general rule of 0.5% per 50°C applicable.
Environment – Instruments are sealed to IP53 standard but can be improved with further measures if required.
Location – Whenever possible, instrument should be located to minimize the effects of vibration, extreme ambient temperatures and moisture. Dry locations away from very high thermal sources (ovens, boilers etc) are preferred. If the mechanical vibration level is extreme, the instrument should be remotely located and connected via a flexible drive shaft.
All instruments are supplied fully weatherproof sealed and should not be disassembled as this would invalidate any remaining warranty. No parts attached to the tachometer are end user replaceable and as such the instrument should always be returned for rectication if deemed to be damaged or operating incorrectly.
Any visible shafts should be kept free of corrosion, lubricated and checked periodically for damage or wear.
All bearings used are fully sealed/waterproof and should last the lifetime of the instrument.
Any indication of condensation or moisture ingress within the instrument could indicate a breach in the sealing properties of the instrument and should be immediately investigated.
Flexible drive shaft maintenance – Periodically the ends of the flexible drive shaft should be disconnected from the tachometer and a small amount of automotive (or equivalent) grease should be applied within & around the internal shaft ends.
Tachometer gearbox (if fitted) – Supplied fully sealed with a long life lubricant applied and should not opened.