Compressor controller replacement and VSD conversion in Finland

How the new controller works

The new controller does not need a variable speed drive. On a fixed-speed compressor it replaces the original controller when that has failed and cannot be repaired or replaced at a reasonable cost. The controller loads and unloads the compressor according to the pressure settings, and once unloaded, the compressor stops when the idle time has passed. The screen, service counters, fault view and fault log, weekly timer, remote run contact, PIN lock and optional remote monitoring work just as on a VSD machine, while speed control, the functions that go with it and the readings that come from the drive are only available on VSD machines. The scope of functions is agreed based on the machine's sensors.

A VSD conversion adds speed control. A fixed-speed compressor always runs at full speed, and air output is limited by unloading or by throttling the inlet. After the conversion, the drive adjusts the motor speed steplessly to the air demand and keeps the pressure at the set point. When demand drops below even the minimum speed, the compressor unloads and stops after the idle time.

The controller is mounted next to the compressor. Its 4.3-inch touchscreen shows pressure, discharge temperature, status and fault cause and a short-term pressure trend – on VSD machines also load, power and energy used today – and pressure settings are changed on the same screen. In a fault, the screen shows the cause and what to check before resetting. When not in use, the controller shows a viewing screen with large pressure and clock readings, and the display also turns off – a touch or a fault wakes it up. Remote monitoring over WiFi with Home Assistant, with history trends and fault notifications, is optional – control always stays local and works without a network connection.

The controller's settings are protected by a service PIN: the compressor is operated as usual, but only the service technician can change pressures, the weekly timer and service counters. Service can still be requested from the lock screen without the code. Service intervals count both running hours and calendar time, whichever comes first – for oil, for example, 2,000 hours or 12 months. Reminders appear on the screen and your phone and, with optional remote monitoring, at Kompressoripalvelu.fi, and the controller logs the 20 most recent faults with time stamps to help with troubleshooting.

VSD conversions typically suit rotary vane and screw compressors with fixed speed and load/unload or inlet throttling control, for example Hydrovane rotary vane compressors. A new controller on its own suits a fixed-speed compressor that is otherwise in good condition but whose controller has failed. Feasibility is always checked per machine. We have developed and tested the VSD solution in our own use.

A weekly timer keeps the compressor running only when compressed air is needed. Weekdays, Saturday and Sunday each get their own running hours, set in 15-minute steps and past midnight if needed; when the time is up, the compressor unloads and stops in a controlled way. A remote run contact – a volt-free contact from, for example, building automation, a door switch or another machine's control – can start the compressor outside the schedule, say for overtime, or keep it locked out, for example by the ventilation or another machine. The contact is a local hard-wired input, so the compressor is not started over the network, and the run enable button on the screen always has the final say.