The deadweight tester apparatus consists of a chamber that is filled with oil free impurities and a piston - cylinder combination is fitted above the chamber as shown in the diagram. The top portion of the piston is attached to a platform to carry weights. A plunger with a handle has been provided to vary the pressure of oil in the chamber. The pressure gauge to be tested is fitted with an appropriate plate.The weight tester is basically a pressure producing and pressure measuring device. It is used to calibrate Transmitters and analog pressure gauges in Toronto. The following procedure is adopted for calibrating pressure gauges. Calibration of the pressure gauge means introducing an accurately known sample of pressure to the gauge under test and then observing the response of the gauge. In order to create this accurately known pressure, the following steps are followed.
The valve of the apparatus is closed then a known weight is placed on the platform. Now by operating the plunger, fluid pressure is applied to the other side of the piston until enough force is developed to lift the piston weight combination. When this happens, the piston weight combination floats freely within the cylinder between limit stops.
In this condition of equilibrium, the pressure force of the fluid is balanced against the gravitational force of the weights plus the friction drag. Now the pressure gauge to be calibrated is fitted at an appropriate place on the dead weight tester. The same known weight that was used to calculate it is placed on the platform. Due to the weight, the piston moves downwards and exerts a pressure of the fluid. Now the valve in the apparatus is opened so that the fluid pressure is transmitted to the gauge, which makes the gauge indicate a pressure value. This pressure value shown by the gauge should be equal to the known input pressure. If the gauge indicates some other value, it is adjusted so that it reads an equal value. Thus, the gauge is calibrated.
Here in Canada, Deadweight testers in Toronto are used to calibrate all kinds of pressure gauges such as industrial pressure gauges, engine indicators, and piezoelectric transducers. It is simple in construction and easy to use. It can also be used to calibrate a wide range of pressure measuring devices. Fluid pressure can be easily varied by adding weights or by changing the piston-cylinder combination. The accuracy of the dead weight tester is affected due to the friction between the piston and cylinder, and due to the uncertainty of the results or values.
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