The Model 4022B is used to check the continuity of connections within an earthing system, generally in substations, terminal stations and power plants. The small carry case houses a mains powered DC injection circuit capable of 1A output. The actual resistance is measured on a handheld readout which is on the end of a test lead. We can supply extension cables up to 100M on a drum so that the resistance can be measured over a long earthing structure.

For practical earth testing using a voltage injection source, it is essential to use a transformer which matches the impedance of the earth loop being tested to the output capability of the injection source.

Typically the earth test circuit consists of the earth grid under test connected to a remote earth grid through an earth path in the ground. To complete the loop, a return connecting path isolated from earth, usually an 'out of service' feeder, is also used. The earth test current is driven around the loop by the secondary winding of the Model 4023 Coupling Transformer which is inserted into the loop.

The primary of the coupling transformer is driven by the Model 4024 or 4024B Injection Unit. Inside the 4023 various secondary taps are brought out to terminals on the front panel via the selector switch. When the correct tap is chosen the Amplifier sees a reflected 1500VA load and it can deliver maximum power.

The Model 4024 is a switch mode voltage source that is used with the Model 4023 Coupling Transformer to produce a high current and low voltage, or high voltage and low current, into an earth loop. The current from the Model 4023 is coupled into the earth loop being investigated.

Frequencies from 45Hz to 65Hz can be generated and the voltage drops around the earth loop are measured with the Model 4025D frequency selective multimeter.

In most cases the operator will try to inject the maximum current into the earth loop being tested since that gives maximum signal for the Model 4025D. For that reason the 4023 has tap settings for earth loop impedances from 0.5 Ohms to 40 Ohms which covers most test situations.
For impedances outside this range the earth loop current will be less than maximum but still sufficient for testing purposes.

The 4024B is similar to the 4024, but is housed in a larger case, and has a larger LCD screen with additional menu options.

This is the latest version of our 4025 series of frequency selective multimeters. In earth testing it is essential to filter out the predominant 50Hz currents that are often present in a typical test situation. This is done by injecting at frequencies other than 50Hz, and making sure the instrument that detects voltages and currents around the loop is tightly tuned to the same frequency.

The 4025D is a frequency selective ammeter and voltmeter used to measure the magnitude and phase of signals produced by the Model 4024 and 4024B Injection Units. The voltmeter part of the 4025D allows touch and step voltages to be measured easily and accurately, which is important for the safety of both the general public and utility personnel.
In earth loops measurements are made of voltage, current and phase angle enabling the impedance of the circuit to be calculated by the software.

A rechargeable battery is used to power the 4025D.

The current input is specifically for use with a Type 545 worm ( Rogowski ) coil or a LEM~flex RR3020 AC current probe . The Rogowski coil and LEM current probe are available as optional accessories. These accessories are very convenient current measuring devices, which can simply be wrapped around current carrying structures. The ability to measure currents in various structures is important in tracking earth currents during investigations. Utility engineers need an accurate picture of the earth currents flowing in substations, power stations and similar large installations when designing protection systems.

The Multimeter operates in the 40 - 69 Hz range, rejecting both 50 Hz or 60 Hz power frequencies. The high quality of the Multimeter’s filters allows it to be used at frequencies up to a limit of 1Hz from the power frequency and still reject power frequency interference.