Test rig determining relaxation performance of leaf springs - preloaded spring is brought under test load which starts counter

The specimen leaf is positioned on two isolated supports. A loading die is located over the centre of the spring. The die has a knife edge and hollow boring through which passes a load-cell probe operated by a press and fitted with a load transducer. The spring is preloaded and an electric circuit is completed through the knife-edge and the spring to a trigger circuit. The press is operated and the load-cell probe is driven downwards through the die to the surface of the spring. This breaks the contact between spring and knife-edge and the trigger circuit freezes the display to indicate the instantaneous load as measured by the transducer and precision bridge.