General Monitors S4000CH Intelligent Combustible Gas Detector

Overview

The General Monitors S4000CH is an intelligent sensor for combustible gas detection from General Monitors, now part of MSA Safety. It is a microprocessor-based transmitter designed to work with General Monitors catalytic bead sensors and to monitor combustible gases and vapours within the lower explosive limit (LEL). The unit processes the sensor signal at the point of measurement, shows the gas concentration on a local display and provides analog, relay and digital outputs to the fire and gas system. Its one-person calibration, event history and remaining sensor life indication were designed to make routine maintenance on large plants faster and more reliable.

Seven Star LLC supplies the General Monitors S4000CH, replacement catalytic bead sensors and accessories to oil and gas operators, refineries and fire and gas contractors in the Sultanate of Oman and across the GCC, with engineering support in Muscat. The detector is installed widely on existing facilities in the region, and we support both spares and new detector loops.

Measurement Principle

A catalytic bead sensor contains a heated active element that oxidises combustible gas on its surface and a matched reference element that does not. As general engineering knowledge, the heat released by combustion raises the temperature and resistance of the active element, and the resulting bridge imbalance is proportional to the gas concentration up to the LEL. The General Monitors S4000CH uses a continuous diffusion, low temperature catalytic bead sensor, and the transmitter converts the bridge signal into a 4–20 mA output proportional to 0 to 100% LEL, with 4 mA at zero and an over-range band of 20 to 22 mA.

For the General Monitors S4000CH, the datasheet gives an accuracy of ±3% LEL up to 50% LEL and ±5% LEL at or above 51% LEL, a zero drift of less than 5% of full scale per year, and response times of T50 below 10 s and T90 below 30 s with 100% LEL methane applied. Sensor life is three to five years. Calibration of the General Monitors S4000CH is virtually automatic: the technician activates the magnetic switch and applies gas, and the unit completes the calibration without a second person in the control room. The detector is also compatible with the Automatic Remote Gas Calibrator for fully automatic calibration.

Engineering Design of the General Monitors S4000CH

All electronics of the General Monitors S4000CH sit in an explosion-proof housing of marine aluminium or stainless steel, 161 mm long, 86 mm high and 104 mm wide, with mounting holes 127 mm apart. The aluminium version weighs 2.5 kg and the stainless steel version 6.4 kg. A three-digit LED display continuously shows gas concentration in normal operation and in gas check mode, calibration prompts in calibration mode, codes in setup mode and eight fault codes, while separate warning and alarm LEDs indicate status. A standard sensor works from −55 to +93 °C, and a high temperature sensor extends this to +200 °C.

The General Monitors S4000CH has four operating modes. In normal mode the alarms are active and the display and current output follow the gas concentration. Gas check mode lets the user apply gas and check the response while alarm outputs are inhibited. Calibration mode calibrates the unit, and setup mode allows the user to review or change the calibration level, energised or de-energised relays, latching or non-latching relays, relay alarm set points and the baud rate, data format and address of each Modbus channel. Setup can be entered with the magnetic switch or by HART or Modbus command.

Key Features

The features and benefits of the General Monitors S4000CH listed in the datasheet are:

• Compatibility with the Automatic Remote Gas Calibrator, allowing fully automatic calibration.
• Event logging that stores fault, gas check, calibration and alarm event history.
• HART and dual redundant Modbus communication for complete status and control capability in the control room.
• An industry standard 4–20 mA output for remote alarm and fault indication.
• Optional warning, alarm and fault relays rated 8 A at 250 VAC or 30 VDC for local alarm capability.
• Calibration, calibration check and setup modes that simplify operation and maintenance.
• Remaining sensor life indication that reduces downtime by estimating when a sensor should be replaced.
• CSA, FM and ATEX approvals, HART registration and SIL 2/3 suitability.

Industrial Applications

Catalytic combustible gas detection remains the reference method for many hydrocarbon gases and vapours, including those for which infrared detection is less suitable, such as hydrogen; the S4000CH carries a CSA/FM classification for Group B and IIB+H2. In Oman the General Monitors S4000CH is used around compressors, separators and pump skids at oil and gas production stations, in refinery and petrochemical process units in Sohar and Duqm, at fuel depots and loading racks, in battery rooms and hydrogen generation areas, and in gas turbine enclosures at power plants. General Monitors S4000CH configurations with relays suit stand-alone local alarm duties, while Modbus and HART versions connect to plant-wide fire and gas systems.

Seven Star LLC supplies the General Monitors S4000CH for new projects and maintenance programmes. Sites using infrared point detection may also run the General Monitors IR400-0-01-1-2-0-1-0 Point IR Gas Detector, toxic gas loops often use the General Monitors 51457-1 H2S Gas Sensor, and for a newer combined platform customers look at the General Monitors TG5000 Toxic and Combustible Gas Monitor.

Technical Specifications

The following data for the General Monitors S4000CH is taken from the manufacturer’s datasheet attached on this page.

How to Order

For a quotation on the General Monitors S4000CH or replacement sensors, send Seven Star LLC the configuration code, housing material and quantity. Our Muscat team will confirm compatibility, share the attached datasheet and support delivery to your site in Oman or anywhere in the GCC.