Tech Page: Electrical Test Instruments
The use of an ETI involves the ability to recognize what is being tested or measured, and to interpret that information and its relationship to overall system operation.
On this Tech Page, we will discuss components that make up electrical circuitry, what is being measured, and the instrumentation used to take these measurements. One reminder before we proceed: While many fine brands and different types of ETIs are available, human appendages are not one of them. Always use extreme caution when working with electricity. Read the instrument’s instructions thoroughly and follow directions diligently.
CIRCUIT COMPONENTSAn electrical circuit is where most of the action takes place when using an ETI. The following are major components of the circuit:
WHAT IS BEING MEASURED?The following is terminology used to describe the rate of current, what pushes it through a circuit, and what forces work to hold it back.
The ETI measures this data. It is up to you, the servicer/installer, to interpret it and apply it to the situation at hand.
Sometimes we need to measure a fraction of an ampere or volt. The following two prefixes are then used:
The following are the two types of current encountered in the hvacr field:
TYPES OF ETIsDigital multimeter (DMM) — This ETI is a combination of several different meters. Its versatility makes it one of the most commonly used meters in the hvacr field today. The number of its functions are in direct correlation with the cost of the meter.
A basic DMM will read ac and dc volts, ohms, and continuity. Additional features may include ac and dc current, frequency, and capacitance.
Typical uses of the DMM are:
Some DMMs will have an “autoranging” feature. The meter automatically sets the range of current or voltage to be measured.
Clamp-on ammeter — This ETI is also very commonly used. A clamp-on ammeter can measure voltage, resistance, and continuity; however, its most distinguishing characteristic is its ability to clamp around a conductor and measure current. This is useful when measuring items like:
Capacitor tester — This ETI measures the capacitance value of a capacitor in microfarads. It also can determine if a capacitor is good or bad.
Compressor analyzer — This ETI tests compressors for continuity, resistance, and amperes. Compressor analyzers contain a start capacitor and a reverse switch to assist in starting single-phase compressors that have become stuck.
Megohmmeter — This ETI measures electrical insulation resistance in ohms or megohms. It can detect motor winding breakdown and buildups of moisture and acid.
Watt meter — This ETI measures watts consumed by an electrical device.
Could you imagine your family doctor not using a stethoscope? Electrical test instruments are like stethoscopes and blood pressure/heart rate monitors. They let you know what is happening within the circuit or system.
Rothacker is a director for AREA51HVAC.COM. For questions or comments on the Tech Page, contact Rothacker at firstname.lastname@example.org (e-mail).
Publication date: 02/18/2002