LPG and natural gas rooms require more than a basic audible alarm. When combustible gas leakage is detected, the system should warn personnel, help remove accumulated gas, and shut off the gas supply when required.
The ANWETECH AT-FG99 is a gas alarm controller designed to work with external gas detectors. When connected to suitable LPG or natural gas detectors, it receives gas concentration information through RS485 communication, displays the alarm condition, activates sound and light alarms, and controls external equipment through relay outputs.
For LPG cylinder rooms, natural gas boiler rooms, gas manifold rooms, commercial kitchens, and gas pipeline areas, the AT-FG99 can form the control center of a gas leak alarm system with exhaust fan and emergency shut-off valve linkage.
A combustible gas detector identifies gas leakage at the detection point. However, sounding an alarm alone does not remove leaked gas or stop gas from continuing to enter the room.
A more practical gas safety system should perform several coordinated actions:
The AT-FG99 supports this type of control sequence through its detector communication, alarm settings, sound and light indication, and relay outputs.
The AT-FG99 is not a standalone LPG or natural gas sensor. Gas detection is performed by the external combustible gas detectors connected to the controller.
The controller is responsible for:
The controller supports up to 99 gas detectors. This makes it suitable for rooms or projects with multiple monitoring points, where several detectors need to be supervised from one central location.
Each detector can be configured with gas type, measurement range, high and low alarm concentrations, linkage output, and enabled or disabled status.
A typical AT-FG99 gas leak control system follows this sequence:
LPG or Natural Gas Detector → AT-FG99 Controller → Sound and Light Alarm → Exhaust Fan → Emergency Gas Shut-Off Valve
The detector continuously monitors the combustible gas concentration in the protected area.
When the gas concentration reaches a configured alarm value, the detector sends the information to the AT-FG99 through RS485 communication. The controller then displays the alarm condition and activates its sound and light warning.
According to the programmed linkage logic, the controller can also activate an exhaust fan or emergency gas shut-off valve through its relay outputs.
The AT-FG99 provides four sets of passive normally open and normally closed relay contacts. The relay contact rating stated in the manual is 250V AC, 5A.
An exhaust fan helps remove leaked gas and reduce gas accumulation inside an LPG or natural gas room.
The AT-FG99 manual includes a typical linkage diagram for a 220V exhaust fan. When the selected alarm output operates, the relay contact completes the fan control circuit and starts the ventilation equipment.
For fan applications, the output can be configured as a maintained output. After the gas alarm is triggered, the relay remains activated until it is manually reset. This allows the fan to continue operating instead of stopping after only a few seconds.
The ventilation sequence can be configured as follows:
The manual states that the AT-FG99 can directly control a device only when the load current is no more than 5A and the load power is no more than 500W.
If the exhaust fan exceeds either limit, it must not be powered directly through the controller relay. An AC contactor or optional linkage control box should be installed between the AT-FG99 and the fan.
In this arrangement, the AT-FG99 relay operates only as a control signal, while the contactor switches the higher-power fan circuit.
Stopping the gas supply is an important emergency action in LPG and natural gas applications.
The AT-FG99 manual provides a typical linkage diagram for a 220V normally open solenoid valve. It also gives a specific warning regarding emergency gas shut-off valves:
The emergency shut-off valve must not be powered continuously.
Many emergency gas shut-off valves require only a short electrical pulse to close. After receiving the pulse, the valve remains mechanically closed and does not require continuous electrical power.
For this reason, the AT-FG99 manual requires the emergency shut-off valve in a combustible gas application to be connected to Output 2.
Output 2 provides a 3-second pulse output.
The operating sequence is:
This pulse control protects the valve from continuous energization and matches the operating principle of a compatible emergency gas shut-off valve.
Before connection, the installer must confirm that the selected valve is suitable for the controller voltage, contact capacity, and 3-second pulse control method.
The AT-FG99 supports high and low alarm settings for each connected detector. These two levels can be used to create a staged response for LPG and natural gas rooms.
A possible control strategy is:
The low alarm can provide early warning and start ventilation before the gas concentration rises further.
Typical low-alarm actions may include:
The high alarm can initiate a higher-level emergency response.
Typical high-alarm actions may include:
The actual alarm values and linkage assignments must match the connected detector, gas type, and project design. Internal parameters should not be modified arbitrarily. The manual recommends that configuration changes be carried out under technical guidance.
When the gas concentration falls below the alarm setting, the AT-FG99 audible alarm stops automatically. However, the visual alarm indication continues to flash, and the linked relay does not reset automatically.
The output must be manually disengaged after personnel confirm that the leakage has been corrected and that the protected area is safe.
This manual-reset logic prevents the system from returning immediately to normal simply because the measured concentration has temporarily decreased.
The emergency gas shut-off valve also requires manual reopening after the gas leak has been resolved.
The AT-FG99 connects to the gas detectors with separate power and communication wiring.
According to the manual:
Correct RS485 polarity and shielding are important. Reversed A/B lines, unsuitable cables, or incorrect grounding may cause unstable communication or communication failure.
The controller’s 24V detector power output is protected by a 10A fuse. If no 24V output is available, the fuse should be checked.
Several points must be confirmed before commissioning the system:
The connected detector must be suitable for the gas being monitored. An LPG application requires a detector configured for the appropriate combustible gas, while a natural gas application requires a compatible natural gas detector.
The AT-FG99 receives and processes the detector signal but does not determine the gas type by itself.
Direct fan control is limited to a maximum load of 5A and 500W. Higher-power fans require an external contactor or linkage control box.
The emergency gas shut-off valve must be compatible with pulse operation. It must not be connected to a maintained output if it is not designed for continuous energization.
In combustible gas applications, the manual specifically assigns Output 2 to the emergency shut-off valve because it provides the required 3-second pulse.
The controller should be powered from a dedicated circuit and should not share its supply circuit with unrelated equipment.
The AT-FG99 should be installed in a control room or instrument panel where authorized personnel can monitor and operate it. It should not be exposed to water, oil, or corrosive gas.
The AT-FG99 fan and shut-off valve control arrangement can be applied in:
The number, type, and installation position of the gas detectors should be determined according to the room layout and project design.
The AT-FG99 combines the main control functions required for an industrial combustible gas alarm system:
These functions allow the controller to coordinate detection, warning, ventilation, and gas shut-off actions from one central panel.
