Pilot LPG Monitoring System

Pilot Gas Monitor
Pilot Gas Monitor

In my mind, the most dangerous thing onboard any boat is the LPG system, as the gas is heavier than air, any leaks tend to collect in the bilges, just waiting for an ignition source. To mitigate this possibility, we’re fitting a gas monitoring system that will sound an alarm & cut off the supply in case of a leak.

Monitor Unit
Monitor Unit

Here’s the monitor itself, the two sensor model. It’s nice & compact, and the alarm is loud enough to wake the dead.

Control Board
Control Board

Not much inside in the way of circuitry, the brains of the operation is a Microchip PIC16F716 8-bit microcontroller with an onboard A/D converter (needed to interface with the sensors), running at 4MHz. The solenoid valve is driven with a ULN2803 Darlington transistor array.
The alarm Piezo sounder can be seen to the right of the ICs, above that is a simple LM7805 linear regulator providing power to the electronics.

Remote Sensor
Remote Sensor

The pair of remote sensors come with 3.5m of cable, a good thing since the mounting points for these are going to be rather far from the main unit in our installation.

Sensor Element
Sensor Element

The sensor itself is a SP-15A Tin Oxide semiconductor type, most sensitive to butane & propane. Unlike the Chinese El-Cheapo versions on eBay, these are high quality sensors. After whiffing some gas from a lighter at one of the sensors, the alarm triggered instantly & tripped the solenoid off.

Solenoid Valve
Solenoid Valve

The solenoid valve goes into the gas supply line after the bottle regulator, in this case I’ve already fitted the adaptors to take the 10mm gas line to the 1/2″ BSP threads on the valve itself. This brass lump is a bit heavy, so support will be needed to prevent vibration compromising the gas line.

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