Riken Keiki SD-3, fixed gas detector for harsh environments
Sottotitolo
Divisions: Fire and Gas
Product Description
The SD-3 series continuously detects combustible gases, toxic gases and oxygen in hazardous areas. Stainless steel housing, IP66/67 protection, operation from -40 to +70 °C.
It is the series Socrate is focusing its Riken Keiki supply on, because it covers the cases where a standard detector does not hold up: cold, corrosion, washdowns, inaccessible installation points and gases outside the usual lists.
At a glance
| Detected gases | Combustible, toxic and oxygen: 76 sensor, gas and range combinations |
| Measuring principles | Non-dispersive infrared, new ceramic catalytic, semiconductor, hot-wire semiconductor, electrochemical |
| Housing | SCS14 stainless steel, equivalent to AISI 316, IP66/67 protection |
| Temperature | From -40 to +70 °C under ATEX and IECEx certification |
| Outputs | Three alternative configurations at order: 4-20 mA with HART 7 (standard), with HART 7 plus relay contacts, or with Modbus RS-485 |
| Certifications | ATEX (DEKRA 24ATEX0017X), IECEx, performance EN 60079-29-1 and EN 45544, MED and SIL2 on specific models |
| Installation | Diffusion, aspiration, remote sensor up to 20 metres, duct insertion |
Key features
F sensors with remaining-life estimation
The detector diagnoses the degradation of its own sensor by analysing the characteristic parameters of the measuring principle, such as zero-output drift or electrolyte level. During calibration it estimates the remaining life by comparing the history of previous calibrations, and signals when the sensor is approaching replacement.
The warning travels as a digital signal over HART or RS-485, so it reaches the control room without a site visit.
Riken Keiki declares a three-year warranty on F sensors, with at least one annual inspection. Some sensors are excluded.
Two-level alarm
Each instrument manages two configurable alarm levels in the combinations high/high-high, high/low and low/low-low.
This separates the warning threshold from the action threshold without doubling the number of installed instruments.
Stainless steel housing for aggressive environments
The body is made of SCS14 stainless steel, equivalent to AISI 316, with IP66/67 protection against powerful water jets and temporary immersion.
It withstands plant washdowns, salty atmospheres and corrosive environments where painted aluminium degrades.
Remote sensor up to 20 metres
In the remote configuration, the SD-3SC main unit stays in an accessible position while the GD-3 series sensor head can be installed up to 20 metres away, with AWG16 shielded twisted cable.
It is designed for points where gas must be detected but no operator can climb up for maintenance: under a floor slab, inside a cabinet, at the top of a column. An optional kit allows direct insertion into a duct.
Integrated intrinsic safety on ECB models
The SD-3ECB, SD-3DECB and GD-3ECB models combine flameproof enclosure and intrinsic safety (Ex db ia IIC T4 Gb). The integrated barrier removes the sintered metal filter in front of the sensor.
That filter retains highly adsorbent toxic gases, slowing down or distorting the reading. Without the filter, the response is more accurate.
Digital integration, not just 4-20 mA
The output is configured at order, choosing one of three options:
- 4-20 mA with HART 7 communication, standard configuration
- 4-20 mA with HART 7 plus three changeover relay contacts (alarm 1, alarm 2, fault)
- 4-20 mA with Modbus communication over RS-485
The three configurations are mutually exclusive: choosing Modbus means giving up HART. It is a decision to take at design stage, because changing it later means replacing the instrument.
Typical applications
- Refineries and petrochemical plants, where stainless steel and a wide temperature range are needed
- Chemical plants with adsorbent toxic gases (carbon disulphide, ethylene oxide)
- Hydrogen production, storage and use, with selective sensors
- Terminals and depots with frequent washdowns and salty atmospheres
- Offshore and marine installations
- Ducts and ventilation systems, with the insertion version
- Inaccessible measuring points, with the remote sensor version
Models and selection criteria
The model is chosen according to the gas and the sampling method. The letter D in the code indicates the aspiration version.
| Diffusion | Aspiration | Principle | Gas | ATEX class | SIL |
|---|---|---|---|---|---|
| SD-3RI | SD-3DRI | Non-dispersive infrared | Combustible, toxic | Ex db IIC T6/T5 Gb | SIL2, SIL3 with redundancy |
| SD-3NC | SD-3DNC | New ceramic catalytic | Combustible | Ex db IIC T5/T4 Gb | SIL2, SIL3 with redundancy |
| SD-3GH | SD-3DGH | Semiconductor | Combustible, toxic | Ex db IIC T5/T4 Gb | Not certified |
| SD-3GHS | SD-3DGHS | Semiconductor | Carbon disulphide only | Ex db IIC T6/T4 Gb | Not certified |
| SD-3SP | SD-3DSP | Hot-wire semiconductor | Combustible, toxic | Ex db IIC T5/T4 Gb | Not certified |
| SD-3EC | SD-3DEC | Electrochemical | Toxic, oxygen | Ex db IIC T4 Gb | SIL2, SIL3 with redundancy |
| SD-3ECS | SD-3DECS | Electrochemical | Hydrogen sulphide only | Ex db IIC T4 Gb | SIL2, SIL3 with redundancy |
| SD-3ECB | SD-3DECB | Electrochemical with barrier | Adsorbent toxic gases | Ex db ia IIC T4 Gb | Certification in progress |
Remote version: SD-3SC main unit combined with a GD-3 series sensor head, available in the same eight variants.
How to choose, in practice
- The gas is a common combustible and SIL is required: SD-3RI (infrared) or SD-3NC (catalytic)
- Hydrogen must be detected without responding to other combustibles: SD-3NC or SD-3SP with selective sensor
- The gas is toxic and highly adsorbent: SD-3ECB, for the integrated barrier without sintered filter
- Oxygen monitoring is required: SD-3EC
- Hydrogen sulphide only: SD-3ECS
- Carbon disulphide only: SD-3GHS
- Limited installation space or inaccessible point: D aspiration version, or SD-3SC with remote head
Infrared and catalytic are not equivalent. Infrared does not get poisoned and works without oxygen; catalytic covers gases that infrared cannot see, such as hydrogen. The choice depends on the gas and on the atmosphere at the measuring point.
Detectable gases
The SD-3 series uses F family sensors. An extract by measuring principle:
| Non-dispersive infrared (IRF) | Methane from 100 %LEL to 100 vol%, propane, isobutane, ethylene, isobutylene, n-hexane, butadiene, carbon dioxide in six ranges from 2,000 ppm to 10 vol%. |
| New ceramic catalytic (NCF) | Methane, ethane, propane, isobutane, acetylene, ethylene, propylene, butadiene, n-octane, toluene, acetone, ethyl alcohol, methyl alcohol, isopropyl alcohol, vinyl chloride, dimethylacetamide. Selective hydrogen from 2,000 ppm to 100 %LEL. |
| Semiconductor (SGF) | Carbonyl sulphide, carbon disulphide, ethylene oxide, hydrogen sulphide. |
| Hot-wire semiconductor (SHF) | Methane, isobutane, ethylene, acetylene, propylene, n-hexane, octane, carbon monoxide, fluoromethane, difluoromethane, hexafluoro-1,3-butadiene, 1,2-dichloroethylene, isopropyl alcohol. Selective hydrogen and deuterium from 500 ppm to 2,000 ppm. |
| Electrochemical (ESF) | Hydrogen sulphide 30 ppm in high-humidity version and 100 ppm, nitrogen dioxide 15 ppm, oxygen 25%. |
Since the January 2026 catalogue edition, electrochemical sensors for carbon monoxide 150 ppm, ammonia in the 75, 150 and 400 ppm ranges and chlorine in the 1.5, 3 and 10 ppm ranges are also available.
Ammonia and chlorine require the models with integrated intrinsic safety barrier, i.e. SD-3ECB, SD-3DECB or GD-3ECB: they are highly adsorbent gases and the sintered filter would distort the reading.
For gases or ranges not listed, the complete list of F sensors includes 76 combinations. Contact us with the gas and range you need.
Dimensions and weight
| Configuration | Dimensions W × H × D | Weight |
|---|---|---|
| Diffusion, standard | 171 × 277 × 127 mm | 6.7 kg |
| Diffusion, tall version | 171 × 322 × 127 mm | 7.3 kg |
| Aspiration, standard | 171 × 289 × 127 mm | 7.0 kg |
| Aspiration, tall version | 171 × 334 × 127 mm | 7.6 kg |
| SD-3SC main unit | 171 × 193 × 127 mm | 6.0 kg |
| GD-3 remote sensor | 125 × 195 × 88 mm, or 125 × 240 × 88 mm | 3.0 kg, or 4.0 kg |
Indicative values, cable glands excluded.
Power consumption by model
| Model | Maximum consumption |
|---|---|
| SD-3RI | 3.8 W |
| SD-3NC, SD-3GH, SD-3GHS | 4.5 W |
| SD-3SP | 3.5 W |
| SD-3EC, SD-3ECS | 2.8 W |
| SD-3ECB | 3.1 W |
| SD-3SC (remote main unit) | 5.0 W |
| GD-3 remote sensor | From 1.0 to 2.0 W depending on model |
Specifications common to the whole series
| Display | 5-digit 7-segment LED, 3 indicator lamps (red, green, yellow) |
| Gas alarm | Two levels (H-HH, H-L or L-LL) |
| Self-diagnostics | System fault (E-9), sensor fault (E-1) |
| Warnings | Sensor remaining life, clock diagnostics, communication diagnostics |
| Standard output | 4-20 mA DC non-isolated linear with HART 7, max load 600 Ω, max resolution 250 divisions |
| Optional output | Modbus over RS-485 half duplex, as an alternative to HART |
| Optional contacts | SPDT, 3 contacts, 250 V 2 A AC or 30 V 1 A DC on resistive load |
| Aspiration flow rate | 0.4-1.5 L/min |
| Power supply | 24 V DC (18-30 V DC) |
| Cable glands | M25 × 1.5 on ATEX and IECEx; optional NPT 3/4, NPT 1/2, M20 × 1.5 adapters |
| Housing material | SCS14 stainless steel, equivalent to AISI 316 |
| Protection | IP66/67 equivalent |
| Temperature | From -40 to +70 °C on ATEX and IECEx; from -20 to +70 °C on Japan Ex |
| Humidity | From 0 to 95% RH non-condensing, subject to individual sensor limits |
| Ex enclosure | Flameproof; flameproof plus intrinsic safety on ECB models |
| CE marking | ATEX, EMC, RoHS directives |
| Communication | HART 7 |
Certifications
Explosion protection
EU type-examination certificate DEKRA 24ATEX0017X, edition 3, issued on 7 April 2026 by DEKRA Certification B.V., notified body 0344, under Directive 2014/34/EU.
| Marking | II 2G Ex db ia IIC T4 Gb and II 2G Ex db [op is] IIC T4 Gb |
| Applied standards | EN IEC 60079-0:2018 + A11, EN 60079-1:2014 + A11, EN 60079-11:2012, EN 60079-28:2015 + A11 |
| IECEx | IECEx certificate of conformity FMG 22.0011X, edition 6, issued on 13 April 2026 by FM Approvals, status Current |
The certificate lists six specific conditions of use, including the prohibition on repairing flameproof joints and the limits on electrostatic discharge. They are available in full in the certificate, which can be downloaded below.
Detection performance
EU type-examination certificate FM22ATEX0019X, issued on 15 April 2026 by FM Approvals Europe Ltd, notified body 2809.
| Standard | Scope |
|---|---|
| EN 60079-29-1:2016 + A1:2022 + A11:2022 | Combustible gases |
| EN 45544-1:2015 and EN 45544-3:2015 | Toxic gases |
| EN IEC 62990-1:2022 + A11:2022 | Workplace atmospheres, toxic gases |
| FM 6320, CSA C22.2 No. 60079-29-1, ANSI/FM/UL 60079-29-1 | Combustible gases, North American market |
| FM 6340, ANSI/ISA 92.00.01 | Toxic gases, North American market |
| EN 50271:2018 | Apparatus using software and digital technologies |
The IECEx certificate FMG 22.0011X covers the same performance tests at international level, for SM-type flammable and toxic gas detectors.
Oxygen and EN 50104. The SD-3 series is not certified to EN 50104, the performance standard for oxygen detectors. If the specification explicitly requires EN 50104 for oxygen monitoring, an alternative model must be evaluated: talk to our engineers before specifying.
Marine use
EC type-examination certificate Bureau Veritas 82838/A0 MED, module B of Directive 2014/90/EU on marine equipment, notified body 2690. Issued on 1 April 2026, valid until 1 April 2031. Category: fixed equipment for oxygen analysis and gas detection, category 3, explosive atmospheres.
Three limits to consider in the specification:
- Partial coverage. The MED certificate only covers models SD-3RI, SD-3NC, SD-3DRI, SD-3DNC, SD-3SC, GD-3RI and GD-3NC.
- Combustible gases only. EN 50104 and IMO MSC.1/Circ.1370 do not apply, because these models are not intended for oxygen detection and measurement.
- No wheelmark with the certificate alone. The production control module D, E or F required by Annex II of the directive is also needed.
Performance declared in the MED certificate: accuracy ±5% of full scale, response time t(90) within 60 seconds, temperature from -40 to +70 °C, IP66/67 protection, 24 V DC power supply from 18 to 30 V.
Functional safety and directives
| Scope | Reference |
|---|---|
| Functional safety | SIL2 according to IEC 61508 on SD-3RI, SD-3NC, SD-3EC and SD-3ECS; SIL3 with redundant architecture. Certification in progress on SD-3ECB |
| Directives | ATEX, EMC, RoHS |
| National explosion protection | Japan Ex |
In aspiration configurations, the associated external unit must also be SIL certified for the function to maintain the declared level.
The flameproof examination covers construction, not detection performance: the performance certificates cover that.
Frequently asked questions
What is the minimum operating temperature of the SD-3 series?
In the ATEX and IECEx certified versions the SD-3 series operates from -40 to +70 °C. In the Japan Ex version the lower limit is -20 °C. Some sensors have narrower ranges: the semiconductor sensor works from -20 to +65 °C and the hot-wire sensor from -30 to +70 °C.
Is the SD-3 series SIL2 certified?
Models SD-3RI, SD-3NC, SD-3EC and SD-3ECS are SIL2 certified according to IEC 61508, and reach SIL3 with redundant architecture. Models SD-3GH, SD-3GHS and SD-3SP are not SIL certified. Certification of the SD-3ECB is in progress. The level of the safety function must in any case be verified case by case on the actual architecture.
How long does an SD-3 sensor last?
Riken Keiki declares a three-year warranty on F sensors, provided that at least one annual inspection is carried out. Some sensors are excluded. The instrument estimates the remaining life during calibration and signals when the sensor is approaching replacement.
Can the sensor be installed away from the detector?
Yes. The remote configuration of the SD-3 series combines the SD-3SC main unit with a GD-3 series sensor head. The head can be installed up to 20 metres away, with AWG16 shielded twisted cable. It is designed for measuring points that are inaccessible for maintenance. An optional kit allows direct insertion into a duct.
Does Socrate provide service on SD-3 detectors?
Socrate performs commissioning, functional testing, scheduled maintenance and calibration on the Riken Keiki SD-3 detectors it has supplied. Spare parts, sensors included, are also handled for Riken Keiki devices purchased elsewhere. The service operates in Italy and at the foreign branches in Libya, Tunisia, Egypt and Greece.
See also
Documentation
- PDFSD-3 series datasheet in English (PC2E-0372, January 2026)
- PDFSD-3 series datasheet in Italian (PC2E-0373, August 2026)
- PDFATEX certificate DEKRA 24ATEX0017X ed. 3
- PDFPerformance certificate FM22ATEX0019X
- PDFIECEx certificate FMG 22.0011X ed. 6
- PDFMED certificate Bureau Veritas 82838/A0
Datasheets are available in English and Italian; certificates are in their original language. For help reading a specification or checking a tender requirement, contact our engineers.
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