Humboldt H-4385 Resistivity Meter - Manual (Page 3)

Description
When combined with appropriate electrodes (pins) and test leads, the H-4385 can be
used to measure earth resistance or the resistance-to-earth of a buried electrode, such as
a ground rod or an anode, for example.
Depending on the application, 4-Electrode, 3-Electrode or 2-Electrode, the H-4385 can
be used to determine the following:
• The average earth resistivity to a specific depth (with the application of an appropriate
multiplier to convert resistance to resistivity, based on the electrode separation
distance) – 4-Electrode Application
• The resistivity of a soil sample, or of a liquid, via an electrolyte (soil/liquid) box
(with the application of an appropriate multiplier to convert resistance to resistivity,
depending on the box geometry) – 4-Electrode Application
• The resistance-to-earth of a buried electrode, such as a ground rod, or an anode, for
example – 3-Electrode Application
• The resistance between two buried electrodes, such as two ground rods, or two
anodes – 2-Electrode Application
The current source in the H-4385, which supplies current between the C1 and C2
terminals (with a load applied), is a 12V(rms) crystal-controlled 97Hz square wave
oscillator and the voltmeter inside the unit, which senses the potential difference (voltage
drop) appearing across the P1 and P2 terminals, employs a very narrow band-pass filter
centered at 97Hz What this means is that resistance measurements taken by the H-4385
are unaffected by any stray interference signals (having frequencies other than 97Hz) that
may be present in the earth during a measurement.
The H-4385 has a resistance measurement range from 0.01Ohm (0.01Ω) to 1.1 MOhm
(1.1MΩ) that is achieved by means of a set of 8 range settings and a system of internal
“standard” resistors. External resistances (resistance values under test) are compared
against the internal “standards, via a null balancing system, resulting in a determination
of the external resistance values.
The H-4385 runs on a set of replaceable C-size alkaline batteries, so there is no
requirement to periodically re-charge the unit or to plug the unit into a power source.
Please see the “Maintenance” section for information on how to replace the batteries.
Operating Instructions
The test lead connections that are made to the “Current” terminals, C1 and C2, and the
“Potential” terminals, P1 and P2, depend on the particular application of the H-4385.
The various connection requirements, as well as the various accessories required in each
application are detailed in the “Applications” section.
Regarding the applications that involve inserting electrodes (pins) into the earth, it is
recommended that the electrodes (pins) be firmly driven into the earth (pins cannot be
loose). Also, in dry soils, it is recommended that the soil around the pins be moistened in
order that reliable (low resistance) contact is made to the surrounding soil.
How to take a resistance reading:
1) Connect the test leads and set up the electrodes (pins) as outlined in the Applications
section for your particular application.