Idec MicroSmart PLCs used on emergency vehicles

Vox VPS Ltd has been producing fire fighting monitors and foam proportioning systems for over 25 years. These have been fitted by a number of crash and fire truck manufacturers in the UK, Europe, USA and Japan. Crash and fire trucks are typically stationed at major and secondary airports, as well as docks and jetties around the world.

The 6inch foam monitor has a capacity of up to 10,000 litres/min and is hydraulically operated for elevation and rotation. Prior to fitting an automatic system, the monitor actions were controlled with electric joystick controllers linked to the hydraulic system either in the cab, on the roof, or both.

Siam Control and Automation of Bromsgrove was approached to provide a fully automatic system incorporating auto-parking and programmable spray patterns. Encoders were attached to sense rotary and elevation position and the signals from these are taken into the high-speed counter inputs of an Idec MicroSmart PLC. A two-channel analogue output card drives analogue meters located in the cab to indicate the positions. When 'park' is selected, the monitor elevates to 10 degrees and rotates to 0 degrees, then lowers to the park position, ready for the vehicle to drive off.

Five spray patterns have been programmed into the PLC and the operator can select one of these, depending on the type of fire. This can be de-selected at any time to control the monitor manually. The spray pattern option is only available when an HMI option is fitted. This is a 6inch monochrome display that shows the monitor position and spray pattern selected.