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Crowcon Blog #4: Chris’s Simple Guide to Gas detector Technology

The arrival of digital technology and communication means that more information can be communicated to a control system, the reduced cable costs create more benefits. So I think it might be useful to provide an overview of the different technical technologies that are available.

Gas safety is very important. Hazards from gases and hydrocarbon vapors, toxic gases such as hydrogen sulphide and environments with low oxygen concentrations, can be potential dangers for workers.

The gas probe of the gas detector is usually connected to a central control system to in which the current gas concentration is located and can immediately trigger any alarm. The detector must measure the gas concentration low enough to react well before the situation becomes dangerous. While gas detectors are located in areas that are believed to be at risk of causing an increase in gas concentrations, the control system must be mounted where it is safe to monitor.

Fixed gas forecasting technology - Chris introduces
Fixed gas forecasting technology – Chris introduces

Detectors are usually connected to the control system via a cable using a contact cable, where each detector connects to a separate input on the control system with an individual cable. These systems use the same signals, which can only transmit a limited amount of information from the detector; Symbolic value (4-20mA), error < 3mA, and overload > 21.5mA

Hart Communication Protocol (www.hartcomm.org) complements common 4-20mA systems by bringing more diagnostic information to the 4-20MA signal. This data can be used to diagnose errors, manage system calibration, and maintain HART-assisted equipment

While the safety function of the detector is still performed by the same 4-20mA signal and the usual controller, HART data allows access to information, including device temperature, serial number, calibration, date of final gas detector calibration, faulty condition, input voltage , line signals, etc.

Modbus is an address-based protocol that communicates with each gas detector using a single address. Information, such as gas concentrations, alarms and error conditions, is stored in the internal memory of the machine, and the ‘Modbus Master’ control system often uses its own connectors to retrieve data – which can be downloaded from the site: www.Modbus.org/docs/PI_MBUS_300.pdf.

Like the HART protocol, Modbus can be used in combination with the same signal to provide more information of the detector, or it can be used as the main media to communicate with the control system, such as PLC (Programmable Logic Controller) or SCADA (Data Monitoring and Collection Control).

Another protocol that is also established is Foundation Fieldbus, which provides opportunities to use alternative cable interfaces. Data can be transmitted via copper or regular fiber optic cables, or via the InSensically Safe (I.S.) interface – can be found at www.fieldbus.org.

This technology allows all detectors to be installed together in one cable rather than the usual way of installing point-to-point connection points. This allows the cost of installing cables to be significantly reduced by connecting multiple detectors on a single cable, where the cable loops from one detector to the next.

Wireless connectivity is a reasonable proposal where running cables for new or additional machines is not feasible. Detectors can be powered on-site (via cable, battery or solar cell) and transmit gas concentration information and status information to the control system via radio signal. Although there are many different wireless products, there is still no “standard” setting for the protocol and frequency of operation, so the suitity will depend on the standards of each region

For new installation equipment, technologies such as Foundation Fieldbus can provide a good overall solution for improving traditional systems. However, each solution has its pros and cons, and is not suitable for each project. Just as always hitting personal safety is always a decisive factor.

Trans by Mr. Manh # TESIN VIETNAM

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