PRESSURE MEASUREMENT AND CALIBRATION (TH2)
EQUIPMENT DESCRIPTION Refer to the drawing on pages 56, 57 and 58. This equipment is a bench top unit designed to introduce students to pressure, pressure scales and common devices available to measure pressure. The equipment comprises a Dead-weight Pressure Calibrator to generate a number of predetermined pressures, connected to a Bourdon gauge and electronic pressure sensor to allow their characteristics, including accuracy and linearity, to be determined. The Dead-weight Pressure Calibrator, Bourdon gauge and pressure sensor are mounted on a common PVC base plate. The electrical console is free standing. The Dead-weight Pressure Calibrator consists of precision ground piston (10) and matching cylinder (11) with a set of weights (12). In normal use the appropriate combination of weights is applied to the top of the piston, to generate the required predetermined pressure, and then the piston is set spinning, to reduce vertical friction, while the readings from the measuring devices are recorded. The operating range of the Dead-weight Pressure Calibrator and instrumentation is 20 kNm-2 to 200 kNm-2. The Bourdon gauge (5) and pressure sensor (6) are mounted on a manifold block (2) with a priming vessel (4) to contain the hydraulic fluid which is chosen to be water for safety and ease of use. A priming valve (7) between the reservoir and the manifold block allows the cylinder, manifold block and gauge on test to be easily primed with the water ready for use. A damping valve (8) between the cylinder and the manifold block allow the flow of water to be restricted to demonstrate the application of damping. An additional isolating valve (9) on the manifold block allows water to be drained from the manifold block or allows alternative devices to be connected for calibration. Such devices can be tested over the range 20 kNm-2 to 200 kNm-2. The Bourdon gauge (5) supplied is a traditional industrial instrument with rotary scale and mechanical indicator. The gauge has a 6” diameter dial that incorporates an arbitrary scale calibrated in degrees of rotation (independent of unit pressure) in addition to the usual scale calibrated in units of kNm-2. A clear acrylic front face allows observation of the Bourdon tube the mechanism that converts motion of the Bourdon tube to rotation of the indicator needle. The electronic pressure sensor (6) supplied incorporates a semi-conductor diaphragm that deflects when pressure is applied by the working fluid. This deflection generates a voltage output that is proportional to the applied pressure. The pressure sensor should be connected to the socket (20) marked ‘Pressure Sensor’ on the front of the console. The power supply, signal conditioning circuitry etc are contained in a simple electrical console (15) with appropriate current protection devices and an RCD (26) for operator protection. The electrical console is designed to stand alongside the Dead-weight Pressure Calibrator on the bench top. All circuits inside the console are operated by a main on/off switch (16) on the front of the console.
The various circuits inside the console are protected against excessive current by miniature circuit breakers, as follows: CONT (27) O/P (28) This breaker protects the power supply and circuits inside the console. This breaker protects the electrical output marked OUTPUT (23) at the rear of the console. The socket is used to power the IFD3 interface used for data logging.
The voltage from the pressure sensor is displayed on a digital meter (17) on the electrical console. An additional conditioning circuit incorporates zero and span adjustments and allows the voltage output from the pressure sensor to be converted and displayed as a direct reading pressure meter calibrated in units of pressure. The zero control (21) and span control (22) are mounted on the front of the console for ease of use. A...