LIFTER AS-VALVE 1632437 - Caterpillar

A volt-Ohm-milliammeter having scales of approximately the following values:AC Volts 0-12, 0-100, 0-300DC Volts 0-50, 0-100, 0-150Ohms X1, X10, X100, X1000DC Amps 0-3A Kelvin or Wheatstone Bridge is necessary to accurately measure the resistance of either the generator revolving field or the stator windings.A 500 or 1000 Volt Megohmeter is used to measure the generator stator and revolving field insulation breakdown resistance.A DC Ammeter with appropriate current shunt.A tong-type Volt-Ammeter with scales 0-600 volts and 0-600 amperes. On generators with high line currents two or more conductors per phase are normally required. To measure line current for these applications, measure the current in each conductor per phase and add the individual conductor currents.A direct reading Tachometer. A 3 or 5 second intergrating tachometer is a relatively precise indicator, providing the drive does not slip. When precise frequency control is required, a direct comparison with utility power can be made.
On generators rated in excess of 600 volts, do not use direct reading test equipment to measure line voltage or line current (even though the instruments have high voltage scales). Potential and current transformers rated for applicable voltage must be used. DO NOT rely on test instrument insulation alone when working on power circuits above 600 volts.
Electrical instruments are not precisely accurate. Five percent difference in readings between two instruments is common. Multi-scale instruments can exhibit five percent difference between scales. Where uniform adjustments are necessary (as in parallel operation), use the same instrument and scale for all voltage adjustments.Many of the test procedures that follow designate the ohmmeter lead polarity (positive or negative) to use on the component being tested. Lead polarity markings of ohmmeter instruments are not to any standard. The lead marked in red, positive or "+" on some volt-ohm-milliammeters is at a positive potential when the instrument is used as an ohmmeter; on others, the lead marked in red, positive or "+" is a negative.
OHMMETER TERMINAL POLARITY CHECK
1-Selector switch. 2-Selector switch. 3-Mark to indicate polarity of ohmmeter leads.Another volt-ohm-milliammeter (multimeter) can be used with the test ohmmeter to determine the correct polarity of the leads.Set one instrument selector switch (1) for DC volts and set the test ohmmeter selector switch (2) for ohms. Alternately connect the leads of both instruments until both instruments indicate a reading (at the same time).The red, positive or "+" lead from the instrument with selector switch (1) set on DC volts is now connected to the test ohmmeter positive lead. Mark the ohmmeter to indicate polarity of the leads (3). The correct positive and negative leads of the test ohmmeter are now identified.Temperature has a notable effect on electrical equipment. Resistance measurements made on a cold unit will be lower than the same measurement made at higher temperatures. Ohmmeters in general are quite inaccurate. Variations of up to 10 percent of published resistances can be expected if the total error of instrument method, temperature and piece part tolerance happen to add in one direction.Index