Diagnostic Technology: Electrical Test Equipment

By Thomas A. Westerkamp  
OTHER PARTS OF THIS ARTICLEPt. 1: Infrared Imagers, Digital Multimeters Among New Tools of MaintenancePt. 2: This PagePt. 3: Specifying Diagnostic Tools for Predictive Maintenance

An AC/DC/volt-ohmmeter with automatic switching is a useful digital multimeter (DMM). Electricians can use it check line voltage, which should be within 10 percent of the rated voltage to prevent damage. Amps should not exceed nameplate full-load amps.

Additional DMM functions include: a digital manometer pressure test; thermocouple thermometer temperature; clamp-on ammeter for live circuit amperes, including narrow jaws and slimmer body for use in crowded electrical panels; and true RMS with temperature, capacitance, duty cycle, and low-pass-filter function that gives accurate readings on high electrical-noise equipment.

With a peak-capture function, an electrician can isolate intermittent malfunctions and transients more quickly, thereby increasing equipment uptime. Data loggers allow continuous monitoring of equipment while an electrician works elsewhere.

A pressure/vacuum module that can measure pressure on the suction and discharge side of the compressor and measure built-in gauge accuracy at the same time enables technicians to perform preventive inspections and diagnose problems.

Vibration Analyzers

These tools measure vibration in reciprocating and rotating equipment over a range of cycles or revolutions per minute. They capture and save measurements for velocity, acceleration, and vibration amplitude and frequency. An amplitude/frequency plot on the analyzer's screen indicates the source, which can include a tool or drive imbalance, looseness, a bent shaft, or bad bearings.

Vibration analyzers can help technicians shorten troubleshooting time and identify specific problem causes quickly before downtime occurs. Linked with a tablet PC, they can save an image as a PDF file and send it just moments later.

The tablet link provides access to the web so the technician can e-mail a vendor, check a vibration guide or severity limits, and optimize the scheduled repair frequency. The unit's connections and large storage capacity enable the technician to access vibration-analysis routes and update equipment vibration history in real time.

Oil Analysis

Oil analyses, such as flash point, cloud point, carbon residue, water and sediment, and particle count, can show the condition of the oil and mechanical wear in a diesel generator, gear box, or transformer. One recent advance in the processes combines oil sampling and gas analysis with a software link.

Consider this situation: If a transformer problem starts immediately after the technician takes an oil sample, the transformer might fail before the next high-cost oil sample is taken months later.

But if a technician has linked a real-time, fixed transformer-gas analyzer to the computerized maintenance management software and the analyzer detects a problem — an increase in gas concentration, for example — the software can issue a warning alerting the technician that the transformer requires instant corrective action. The oil sampling occurs only when needed, rather than on a fixed frequency.

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  posted on 10/1/2012   Article Use Policy

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