Digital resistance meters are instruments that measure electrical resistance. They use solid-state components and display values digitally. Resistance, which is measured in ohms, is the opposition to the flow of electric current of a conductor.

Typically, digital resistance meters are powered by an internal battery that applies a small voltage to the circuit being tested. The positive lead is connected to the circuits positive side and the negative lead is connected to the circuits ground.

The current is then measured and the resistance calculated. Zero resistance indicates a short. Infinite resistance indicates an open. Often, resistance readings that exceed product specifications are caused by a faulty component or problems such as burnt contacts, corroded terminals, or loose connections. To maintain accuracy, digital resistance meters require regular calibration that consists of connecting the two leads together and zeroing the meter with the adjustment knob.

Ohmmeter principles. Video Credit: NTS Press / CC BY 3.0

Specifications

• Digital resistance meters typically display between three and seven digits along with a leading number such as 0 or 1.
• Four-wire systems minimize voltage drops in the test leads and record highly accurate measurements. Benchtop, rack mounted, and handheld devices are commonly available.
• Battery powered units do not require plug-in power.
• Digital resistance meters with audibility continuity beep when the probes touch.
• Devices with analog bar graph capabilities display status readings such as battery power, signal level, and continuity.
• Some digital resistance meters allow users to adjust the sampling rate or provide internal memory. Others include an auto-ranging feature that automatically adjusts the measurement range.
• Output options include general-purpose interface bus (GPIB), binary coded decimal (BCD), and digital-to-analog (DA). RS232 is a standard communication protocol for serial ports. IEEE 488 is a standard communication protocol for parallel ports.

Applications

Digital resistance meters interface to computers and include integral monitoring software for applications such as data acquisition.  Programmable digital resistance meters allow users to set values that trigger monitoring routines. Data storage, logging, and removable data storage devices are often available.  Some digital resistance meters are used to monitor devices such as resistance temperature detectors (RTDs). Others are used to monitor electronic components such as transistors or diodes.

Standards

A-A-59320 - Ohmmeter

A-A-59322 - Ohmmeter

A-A-59381 - Ohmmeter

ESD TR50.0-02 - High resistance ohmmeters - voltage measurements

Image credit:

Tinsley Precision Instruments