How the Resipod Resistivity Meter Works on Concrete

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The person typing resipod resistivity meter wants to know what the instrument measures, how it is used on concrete, and what its readings mean. The Resipod is a four-point surface resistivity meter for concrete structures and lab specimens. It measures electrical resistivity in kilohm-centimeters, and both accessible sources give a usable range of about 1 to 1000 kOhm-cm. This guide explains the method, the steps for a field check, and the points where the two sources differ.

Quick answer

• The Resipod sends a small current through four probes in a line and measures the voltage between the two inner probes. The reading is resistivity in kOhm-cm, not a simple resistance.
• Both sources give a range of about 1 to 1000 kOhm-cm. The Stuart Hunt listing gives 0.1 to about 1000 kOhm-cm.
• The two sources name different standards. Stuart Hunt cites AASHTO Provisional Standard TP 95-11. Gilson cites AASHTO T 358 and says an ASTM standard is pending. Check the standard your project requires before you use the meter.

How we chose

We chose the Resipod because the name is specific and two listings describe the same concrete resistivity meter: Stuart Hunt and Gilson. We opened both on 2026-10-30. Both listings give enough detail to compare the range, the probe method and the standards. We did not use search snippets, star ratings or retailer prices. Where the listings differ, we report both.

What resistivity means on concrete

Electrical resistivity describes how strongly a material resists the flow of current. Concrete conducts current through the water in its pores, so the resistivity depends on how wet the concrete is, how dense the paste is, and how many ions the pore water holds. The Stuart Hunt listing states that current in concrete is carried by ions in the pore liquid. The Gilson listing says surface resistivity is linked to how easily fluid moves through the concrete and how well it resists chloride penetration.

That link is why the reading is useful. A dense, low-permeability concrete usually reads higher, and a porous concrete with a wet, ion-rich pore solution usually reads lower. The Stuart Hunt listing links the resistivity to the likelihood and rate of corrosion, to the rate of chloride diffusion, and to early compressive strength. These are the uses the listing names, and we report them as the listing’s claims.

How the four-point probe works

The Resipod uses a four-point Wenner array. The two outer probes apply current, and the two inner probes measure the potential difference between them. Because the voltage is measured away from the current electrodes, the reading depends on the material rather than on the contact resistance at the surface. Both listings describe this arrangement.

The resistivity that the meter calculates depends on the probe spacing. The Stuart Hunt listing says the calculation depends on spacing but does not state a value. The Gilson listing gives the spacing for each model. The HM-952 has a fixed 1.5 inch (38 mm) spacing per AASHTO T 358. The HM-954 uses 1.97 inches (50 mm). An optional HMA-844 geometric accessory is adjustable from 1.57 to 2.76 inches (40 to 70 mm). Use the probe set that matches the spacing your standard or project requires.

The Gilson listing states the test current is variable from 10 to 50 microamps, or a full 200 microamps. The Stuart Hunt listing gives a resolution of plus or minus 0.2 kOhm-cm or 1 percent at 200 microamps, and plus or minus 0.3 kOhm-cm or 2 percent at 50 microamps. These figures describe how precisely the meter resolves a reading at each current setting.

Step-by-step: a field check on concrete

Step 1: choose the probe set and spacing

Select the probe set that matches the standard for your project. If the listings’ spacing does not match your required standard, do not substitute a spacing from a listing. Confirm the requirement before you start.

Step 2: prepare the surface

The Gilson listing describes small water reservoirs at each contact point and foam contact pads. Wet the pads and check that each probe makes firm contact with the surface. A dry contact gives an unstable reading.

Step 3: set the test current

Choose a current from the 10 to 50 microamp range or the 200 microamp setting, according to the listing. Start at a setting that gives a stable reading on your surface, and note the setting with each result.

Step 4: take readings and record them

The Gilson listing says the meter stores up to 500 readings and works with Resipod Link Windows software for data download. The Stuart Hunt listing gives a USB connection, Resipod Link PC software and more than 50 hours of battery autonomy. Save the readings with the location, the probe spacing and the current setting, because a result without these details cannot be compared with another.

Calculating and reading the result

The meter reports resistivity in kOhm-cm, which is a material property rather than a resistance in ohms. A low value suggests a wet or ion-rich pore solution, and a high value suggests a dense, dry or low-permeability concrete. Both listings place the measurement range at about 1 to 1000 kOhm-cm, with the Stuart Hunt listing giving the lower limit as 0.1 kOhm-cm.

The reading should be compared with a reference for the same mix and the same moisture condition. We do not offer a threshold value for corrosion risk in this guide, because the sources we opened do not give one. The Gilson listing describes the meter as an alternative to ASTM C1202 rapid chloride permeability testing, and it describes the meter’s use for laboratory cylinders and mapping of existing structures. Those uses are the listing’s descriptions, and they do not replace the standard’s own procedure.

Where the two sources disagree

The clearest difference is the standard. The Stuart Hunt listing cites AASHTO Provisional Standard TP 95-11. The Gilson listing cites AASHTO T 358, and it also mentions an ASTM standard as pending. These are different documents, and the listing text does not explain how they relate. Check which standard your project or agency requires before you choose a procedure.

The probe spacing is also described differently. The Stuart Hunt listing gives two variants, a 2 inch (50 mm) spacing and a 1.5 inch (38 mm) spacing, but it does not say which dimension each name refers to. The Gilson listing states the spacing for each model directly. We use the Gilson figures for spacing and report the Stuart Hunt figures only as listed.

The Stuart Hunt listing describes the meter as the successor to the CNS Farnell resistivity meter and says the meter has been used in highway department studies. We could not confirm those history claims from any source outside the listing, so this guide does not repeat them as fact.

Safety and handling notes

The Resipod is a field instrument for concrete work. The listings describe it as waterproof and designed to float, with an IP67-rated enclosure in the Gilson listing. Keep the USB connection and the charger away from standing water, and dry the probes after each use. Do not use the meter near energized equipment unless the site’s procedure allows it, and follow the rules for the structure you are testing.

What we could not verify

• The Stuart Hunt listing does not state a probe spacing value. We could not confirm the spacing from that page alone.
• The two listings name different standards. We could not confirm from the pages we opened whether TP 95-11 and T 358 describe the same procedure.
• Neither listing gives a corrosion threshold in kOhm-cm. We do not state one.
• The history claims about highway department use and the CNS Farnell successor appear only in the Stuart Hunt listing.
• Neither listing gives a full accuracy statement for every range, so this guide reports only the resolution figures given.

FAQ

What does the Resipod measure?

It measures electrical resistivity of concrete, in kOhm-cm, using a four-point Wenner probe.

What is the measurement range?

Both sources give about 1 to 1000 kOhm-cm. The Stuart Hunt listing gives a lower limit of 0.1 kOhm-cm.

What is the probe spacing?

It depends on the probe set. The Gilson listing gives 1.5 inches (38 mm) for the HM-952, 1.97 inches (50 mm) for the HM-954, and an adjustable range of 1.57 to 2.76 inches for the optional geometric accessory.

Which standard does it follow?

The sources name different standards. Stuart Hunt cites AASHTO TP 95-11, and Gilson cites AASHTO T 358 with an ASTM standard pending.

Can the readings be used for a corrosion decision?

The listings describe corrosion-related uses, but they do not give a threshold. Use the procedure and criteria that your project or standard requires.

Related reading on this site: Klein non-contact voltage detectors and how a current clamp works.

Bottom line

The Resipod is a four-point concrete resistivity meter that reports values in kOhm-cm over about 1 to 1000 kOhm-cm. Match the probe spacing to the standard your project requires, and confirm which AASHTO or ASTM procedure applies before you take a reading you intend to use.

Sources

• Stuart Hunt, Resipod Resistivity Meter product page: https://www.stuarthunt.com/store/product/resipod-resistivity-meter (opened 2026-10-30)
• Gilson, Resipod Concrete Resistivity Meter product page: https://globalgilson.com/resipod-concrete-resistivity-meter (opened 2026-10-30)