RKI GX-3R vs GX-3R Pro: how many sensors each has, what the fifth channel adds, and which parts they share
The GX-3R has three sensor slots and reads four gases: a dual electrochemical H2S/CO sensor in slot 1 (or a CO-only, H2S-only or hydrogen-compensated CO sensor), a catalytic combustible sensor in slot 2 and an electrochemical oxygen sensor in slot 3. The GX-3R Pro has four slots and reads up to five gases: the same three plus a fourth slot for a toxic or infrared sensor, which RKI lists as HCN, NH3, NO2, PH3, SO2 or CO2 in percent or ppm. The Pro also adds Bluetooth to RKI’s RK Link phone app, a man-down alarm, a full-dot display that lights and rotates on its own, and the choice of a Li-ion or alkaline pack, at 4.58 ounces against the GX-3R’s 3.52. Run time is 25 hours on Li-ion for both with electrochemical sensors; the Pro drops to 16 hours with the infrared CO2 sensor. Both carry ATEX, CSA, IECEx and MED approvals, IP-66/68, a 23 ft drop rating and a three-year warranty including sensors, and both take the same ESR series sensors, which RKI states are also used in the GX-Force, 04 Series and GX-6100.
RKI Instruments 72-PAX-D GX-3R Pro 4-Gas Monitor, LEL/O2/H2S/CO, Li-ionGX-3R Pro four-gas configuration: four slots, the fourth free for a toxic or CO2 sensor (RKI data)Why the slot count is the question to ask. The two instruments share sensors, chargers, calibration kits and the SDM-3R dock, so the price difference buys three things: the fourth slot, the radio and the man-down alarm. RKI’s own description of the GX-3R is that two of its sensors are combined, the H2S and CO in one dual micro-sensor, which is how a monitor with three physical sensors reads four gases and is the answer to the question people type in. The Pro keeps that and adds a slot RKI calls interchangeable: a crew that needs sulfur dioxide at a refinery, hydrogen cyanide in a fire investigation or carbon dioxide in a brewery or a digester adds the sensor without changing instruments. Both instruments count as four-gas confined space monitors under 1910.146; neither has a pump built in, and both take RKI’s RP-3R clip-on pump or a hand aspirator for the pre-entry test.
Side by side, in RKI’s figures
From the two product pages and RKI’s articles.
What RKI states about the sensors themselves
From RKI's pages:
- The H2S and CO sensors are one combination micro-sensor in slot 1 of both instruments; RKI also offers CO-only, H2S-only and hydrogen-compensated CO sensors for the slot.
- The LEL sensor has two active filaments: if one is poisoned by silicone the second takes over.
- The oxygen sensor is electrochemical with a 3 to 5 year life span (RKI's GX-3R page and its GX-3R vs GX-2009 article).
- Sensors are field replaceable, RKI states in less than 60 seconds, and interchangeable across the GX-3R, GX-3R Pro, GX-Force, 04 Series, GasWatch 3 and GX-6100.
- Ranges: LEL 0 to 100 percent (1 percent steps), O2 0 to 40.0 percent (0.1), H2S 0 to 200.0 ppm (0.1), CO 0 to 2,000 ppm (1); response within 30 seconds (T90).
- The GX-3R replaced the GX-2009: RKI's comparison lists 25 hours against 20 on the GX-2009's NiMH cells, IP-66/68 against IP-67, a 23 ft drop against 1 m, and the hydrogen-compensated CO option.
Ranges and preset alarms shared by both instruments
| Gas and sensor | Measuring range (increment) | Accuracy statement | Preset gas alarms (user adjustable) | TWA and STEL alarms |
|---|---|---|---|---|
| LEL (CH4 or HC), catalytic | 0 to 100% LEL (1% LEL) | ± 5% of reading or ± 2% LEL | 1st 10% LEL, 2nd 25% LEL, 3rd 50% LEL, over 100% LEL | — |
| Oxygen (O2) | 0 to 40.0% vol (0.1%) | ± 0.5% O2 | Low 19.5%, low-low 18.0%, high 23.5%, over 40.0% | — |
| Hydrogen sulfide (H2S) | 0 to 200.0 ppm (0.1 ppm) | ± 5% of reading or ± 2 ppm | A1 5 ppm, A2 30 ppm, A3 100 ppm | TWA 1.0 ppm, STEL 5.0 ppm |
| Carbon monoxide (CO) | 0 to 2,000 ppm (1 ppm) | ± 5% of reading or ± 5 ppm (± 2 ppm, hydrogen-compensated sensor) | A1 25 ppm, A2 50 ppm, A3 1,200 ppm | TWA 25 ppm, STEL 200 ppm |
Source: RKI Instruments GX-3R Pro product page and specification table (rkiinstruments.com/product/gx-3r-pro-gas-detector, rkiinstruments.com, fetched Nov 8 2026); RKI Instruments 04 Series product page and specification table (rkiinstruments.com/product/04-series-single-gas-detectors, rkiinstruments.com, fetched Nov 8 2026)
RKI run times and sampling, as printed
| Model | Gases | Sampling | Power and run time | Weight | Ingress rating | Approvals |
|---|---|---|---|---|---|---|
| GX-3R Pro | 1 to 5 (LEL, O2, H2S, CO plus one toxic or IR) | Diffusion (RP-3R pump optional) | Li-ion 25 h or alkaline 16 h with an EC fifth sensor; 16 h / 7 h with the IR CO2 sensor | 4.58 oz | IP-66/68 | ATEX, CSA, IECEx, MED |
| GX-3R | 4 (LEL, O2, H2S, CO) | Diffusion (RP-3R pump optional) | Li-ion, approx. 25 h after a 3 h charge | 3.52 oz | IP-66/68 | ATEX, CSA, IECEx, MED |
| GX-Force | 1 to 4 (LEL, O2, H2S, CO) | Internal pump, 100 ft sample range, 0.5 L/min | Li-ion, approx. 30 h; USB Type-C | 9.87 oz | IP67 equivalent | IECEx, ATEX, C QPS US Class I Div 1 Groups A, B, C, D; Class I Zone 0 |
| 04 Series (HS-04, CO-04, CO-04C, OX-04, CX-04, SC-04) | 1 (2 for the CX-04) | Diffusion | 2 AAA alkaline; 9,000 h HS-04 and CO-04, 6,200 h CO-04C, 3,000 h OX-04 and SC-04, 4,600 h CX-04 | 2.8 oz | IP-67 | ATEX, IECEx, QPS C/US Class I Div 1 Groups A, B, C, D |
Source: RKI Instruments GX-3R Pro product page and specification table (rkiinstruments.com/product/gx-3r-pro-gas-detector, rkiinstruments.com, fetched Nov 8 2026); RKI Instruments GX-3R product page and specification table (rkiinstruments.com/product/gx-3r-gas-detector, rkiinstruments.com, fetched Nov 8 2026); RKI Instruments GX-Force product page and specification table (rkiinstruments.com/product/gx-force-portable-4-gas-monitor, rkiinstruments.com, fetched Nov 8 2026); RKI Instruments 04 Series product page and specification table (rkiinstruments.com/product/04-series-single-gas-detectors, rkiinstruments.com, fetched Nov 8 2026)
Questions people ask
How many physical sensors does the GX-3R have?
Three sensor slots reading four gases: a dual H2S/CO electrochemical sensor in slot 1 (or a CO-only, H2S-only or hydrogen-compensated CO sensor), a catalytic LEL sensor in slot 2 and an electrochemical oxygen sensor in slot 3, as RKI Instruments’ GX-3R page lists them.
How many sensors does the GX-3R Pro have?
Four slots for up to five gases: the same three plus a fourth slot for a toxic or infrared sensor, which RKI lists as HCN, NH3, NO2, PH3, SO2 or CO2 in percent or ppm.
What sampling method does the GX-3R use?
Diffusion: the gas reaches the sensors through the instrument’s face as it is worn. RKI’s RP-3R is a clip-on battery pump that turns a GX-3R or GX-3R Pro into a sample-draw unit with hoses from 10 to 100 ft, and a hand aspirator is the alternative.
What is the difference between the GX-3R and GX-3R Pro?
The Pro adds the fourth sensor slot, Bluetooth to RKI’s RK Link app, a man-down alarm, a full-dot display that lights and rotates, and a choice of Li-ion or alkaline pack, at 4.58 ounces against 3.52. Both run about 25 hours on Li-ion with electrochemical sensors; the Pro drops to 16 hours with the infrared CO2 sensor.
Can I put a GX-3R Pro sensor in a GX-3R?
The LEL, oxygen and H2S/CO sensors are shared and interchangeable across the GX-3R, GX-3R Pro, GX-Force, 04 Series and GX-6100 by RKI’s statement; the fourth-slot toxic and infrared sensors fit only instruments with a fourth slot.
How long does the battery last?
About 25 hours on the Li-ion pack for both after a 3-hour charge (RKI’s pages); the Pro runs 16 hours on alkaline with an electrochemical fifth sensor, and 16 hours Li-ion or 7 hours alkaline with the infrared CO2 sensor, less with Bluetooth on.
Is the GX-3R intrinsically safe?
Both carry ATEX, CSA, IECEx and MED approvals by RKI’s pages, which is the third-party verification RKI’s FAQ says OSHA looks for; the GX-Force and 04 Series are the models RKI’s pages describe with the words intrinsically safe and a QPS Class I, Division 1 listing.
Where are they made?
RKI’s product data file lists Japan as the country of origin; RKI Instruments is the North American partner of Riken Keiki of Japan, headquartered in Union City, California.
Do they have a pump?
Not built in. Both are diffusion units; the RP-3R clip-on pump or a hand aspirator adds sample-draw capability. RKI’s GX-Force is the model with an internal pump and a 100 ft sample range.
What is the warranty?
Three years on material and workmanship including sensors, by RKI’s pages; the ammonia and chlorine sensors and the PID carry one year.
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