TorqSense transducer improves validation test efficiency

Grundfos designs and builds a vast range of electric and diesel-driven Firesets that form the heart of many sprinkler systems. These Firesets have sophisticated control systems that activate automatically when a fire is detected. They also have to meet the requirements of the demanding Loss Prevention Certification Board relating to fire protection of buildings and their occupants.

Huw Lloyd, Engineering Manager for Grundfos Pumps Ltd, explains: "Even a moderate-sized system can have many of the sprinklers heads. Typically just a few of these will go off to contain a small local fire, but the Fireset has to be able to deliver a predetermined pressure range to every head, even if they are all deployed. It is important to make sure everything is correct before the Fireset leaves the factory; after all, lives are at stake here."

Grundfos therefore subjects each Fireset to a rigorous performance test prior to despatch to prove that it does exactly what it is supposed to do.

Fireset architecture

The Fireset set is basically a diesel or electrically driven pump that is sized to comfortably meet maximum demand. Its control system is designed to start the system automatically when a fire is detected and then control the pressure of water needed to address the fire.

Huw Lloyd says: "We test about 100+ Firesets systems each year, which means the test area is in continuous use and we have to constantly look to improve our operating efficiency.

"The critical part of the testing process is to confirm that the pump's performance is being achieved, and to do this we need a torque meter that will withstand the tremendous amount of vibration present. We chose a torque meter that we were advised would withstand the vibrations of a tractor ploughing a field - but this was not up to the job, so we asked sensor expert Morton Moeller of Sensor-Technik to come up with a better idea."

Moeller almost immediately recommended a TorqSense unit made by Sensor Technology. TorqSense units are superbly robust and have a first-rate track record in arduous installations. They also have other attractions that are said put them 'head and shoulders' above alternative sensors.

Advantages of TorqSense

Moeller says: "The Grundfos specification was very wide, because their systems vary so much in size. I set myself the challenge of covering this with a single sensor so that Huw Lloyd and his team did not have to spend time swapping between big, medium and small units each test, and also to contain the procurement costs."

Another great attraction is that the TorqSense device does not have to be physically connected to the Fireset under test by slip rings. Instead it monitors the torque via radio waves.

How it works

A shaft deforms very slightly when it rotates, with the amount of deformation being proportional to the torque. The TorqSense measures the deformation so that it can calculate torque. To do this, two tiny piezo-electric combs are glued to the surface of the shaft at right angles to one another; shaft deformation expands one comb and compresses the other. The radio frequency signal emitted by the Torqsense is reflected back by the combs, with its frequency changed in proportion to the combs' deformation.

Moeller explains: "The procedure to set up the TorqSense for each new test is to point it at the Fireset. The old system took several hours of concentrated effort by a couple of Grundfos test engineers, and it needed an awful lot of resetting during the test. These savings alone represent a significant efficiency gain for Grundfos."

Huw Lloyd is equally exuberant about the installations: "We have been using the TorqSense for the best part of two years now, so we have tested many different Firesets - big, small, simple and complex. The best thing I can say about it is that we had forgotten it was there; it does its job perfectly, time after time."

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