Multimeters

Multimeters are electrical testers that combine several measurement functions into one unit making it an essential instrument for testing or troubleshooting electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems. Like most things, multimeters range in price and quality. From inexpensive handheld meters best suited for home use to highly accurate benchtop models designed for the most sophisticated testing, multimeters boast an impressive range of functions and features making it simple to find one that fits any need and any budget.

Multimeters are closely related to clamp meters though they serve different objectives. Each capable of multiple electrical measurements, clamp meters are primarily current-measuring devices with some voltage-measuring ability while multimeters are voltage-measuring instruments with some current-measuring ability. An electrical technicians well-stocked toolkit includes both a multimeter and a clamp meter.

Multimeter Technology

Since multimeters have the capability to measure different electrical parameters, their design must include the proper sensors, rectifiers, switches, and resistors for each function. In all types of multimeters, the quality of the switching elements is critical to stable and accurate measurements. Stability of the resistors is a limiting factor in the long-term accuracy and precision of the instrument.

Multimeters come in two basic designs, analog and digital. The primary difference between the two is the display, an analog multimeter uses a needle to show the value, while a digital multimeter will show the results as numbers on a screen. There are pros and cons to both devices.

Analog vs digital

Early multimeters were all analog and, though digital multimeters (or DDMs) are now far more common, analog meters still have their place… and their fans.

Analog multimeters utilize D'Arsonval or Weston meter movement which relies on DC current passing through a coil and magnet assembly to swing a pivot-mounted needle. The amount of current flowing through the coil determines how far the needle will swing, providing proportional measurement rather than just detection. Depending upon the type of measurement (voltage, resistance, current) or range, series resistors, shunt resistors, rectifiers, or switches are used to enable the measurement.

Since analog multimeters use a needle moving along a scale to indicate the measurement value, they are preferred in some situations. When working in an awkward location or with a live circuit in cramped conditions, for instance, many technicians find the needle easier to view without having to look directly at it. The needle response on an analog meter is also superior for monitoring a rapidly fluctuating value.

Analog meters also have a much lower impedance than digital multimeters providing a more substantial load than their digital counterparts. This can be very important if measuring something that is open circuited.

Digital multimeters use their own sets of resistors and amplifiers to offer a much wider range of measurements and functions. Modern digital multimeters feature higher accuracy, dependability, more advanced features, and greater ease-of-use than analog meters making them a more versatile choice for most applications.

Multimeter Features

Multimeters are often available with a number of features that make it easier to take accurate readings and handle the resulting data. Of course, higher end meters are more likely to include these advanced functions.

True RMS: Since alternating current reverses directions several times per second, it is represented as a sine wave. Because the amplitude of the sine wave changes continuously over the wave period, current measurements may vary quite a bit at different points in time. True-RMS (root mean square) converts AC signals into DC signals of equivalent value for more stable and accurate AC readings.

IP rating: Ingress Protection Rating classifies and rates the degree of protection of enclosures against the intrusion of moisture and foreign bodies. Adequately protected instruments are suitable for use in a wider range of environments. NEMA ratings are another enclosure rating system that is commonly used.

PC interface: Increasingly, multimeters are including serial ports (PC interfaces) as a means to easily transfer data from the meter to a computer where further analysis or report generating can occur. Common interfaces include Ethernet, USB, FireWire, RS-232, RS-485 or Bluetooth. Often, software is also available to help organize data once it has been transferred to a computer.

Data logger: Internal memory capable of holding a number of measured values for later recall.

Inrush: The Inrush function provides users an accurate measurement of high current surges that flow into motors during startup. This measurement can be critical when troubleshooting problems such as nuisance trips of over-current protection devices.

Autoranging display: Autoranging units automatically sets the correct measurement range saving users from having to adjust switch positions while trying to position the clamp and take a measurement.

Multimeter Measurements

Multimeters are designed to perform a number of functions. Nearly all multimeters will include voltage, resistance, and current measurements. More advanced models also include a number of additional measurements that increase the versatility of your instrument.

• AC/DC current: Current, measured in amperes, is the flow of an electric charge. Current can be used to generate heat as well as magnetic fields, which are widely used for motors, inductors, and generators.
• AC/DC voltage: Voltage, measured in volts, is the difference in electrical potential of a unit charge transported between two points, or more simply, how much electrical energy is delivered if a certain number of electrons are transmitted through a circuit. Voltage can represent either a source of energy or energy used , stored, or lost.
• Resistance: Resistance, measured in ohms, is the opposition to passage of an electrical current through a conductor. Resistance is determined by the material and shape of the conductor.
• Continuity: Continuity is a quick "pass/fail" resistance test that distinguishes between an open or closed circuit. Generally, a continuity test emits a beep when a closed circuit is detected eliminating the need to look at the meter as the test is performed.
• Capacitance: Capacitance, measured in farads, is the ability of an object to store an electrical charge. Any object that can be electrically charged exhibits capacitance.
• Frequency: Frequency, measured in hertz, refers to the rate at which oscillations of alternating current occur in an electric power grid. Generally, 220-240 VAC uses a 50 Hz frequency while 100-120 VAC uses 60 Hz.
• Power Factor: Power factor is an advanced measurement defined as the ratio of real power flowing to the load, to apparent power in the circuit. In an electrical system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred.
• Temperature: Many multimeters accept input from temperature probes or thermocouples for contact temperature measurements.

Things to Consider When Selecting a Multimeter:

• What measurements and ranges are needed?
• Does the meter need protection from dirt or moisture (IP or NEMA ratings)?
• What resolution and accuracy are required?
• What accessories (test leads, probes, etc.) are needed?
• Does the meter have the correct safety rating for the work you are doing?

If you have any questions regarding multimeters please don't hesitate to speak with one of our engineers by e-mailing us at sales@instrumart.com or calling 1-800-884-4967.