GB2129170A

GB2129170A - Improvements in or relating to pressure controllers

Info

Publication number: GB2129170A
Application number: GB08327757A
Authority: GB
Inventors: John Lawton Sharp
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1982-10-21
Filing date: 1983-10-17
Publication date: 1984-05-10
Also published as: GB8327757D0; GB2129170B

Abstract

The present invention provides a fast response gas pressure controller for pressure transducer calibration. The pressure controller comprises a manifold (1) for connection to a high pressure gas source, a plurality of primary ports each connecting the manifold to a chamber (6), wherein each primary port has a fixed orifice plate (10) and a solenoid operated shut-off valve (2) for controlling the flow through the port, and the flow areas of the orifice plates extend over a range of different sizes, a pressure transducer (8) arranged to measure the chamber gas pressure, and electronic control means (9) for controlling the progressive operation of the valves in response to the difference between the output from the pressure transducer and a pressure demand signal (7). The controller also has auxiliary ports (10f, 10g) connected to a low pressure P2 or atmosphere whereby the pressure in the chamber may be reduced. <IMAGE>

Description

SPECIFICATION Improvements in or relating to pressure controllers The invention relates to pressure controllers and particularly, though not exclusively, relates to calibration pressure controllers for providing steady, accurately known pressures for the calibration of pressure transducers.

A known pressure controller comprises a pressure chamber to a manifold having a gas inlet valve, a gas pressure transducer having an electrical output and arranged to measure chamber gas pressure, an actuator connected to receive the transducer output signal and having an output proportional to the difference between the output signal and a reference signal, wherein the actuator controls the position of the inlet valve and admits gas from a high pressure source until the pressure in the manifold and the chamber reaches the reference pressure.

The present invention provides a pressure controller having a fast response time and improved accuracy, and in particular provides a fast response pressure controller for pressure transducer calibration.

According to the present invention m pressure controller comprises a manifold for connection to a high pressure gas source, a plurality of primary ports each connecting the manifold to a chamber, wherein each primary port has a fixed orifice plate and a solenoid operated shut-off valve for controlling the flow through the port, and the flow areas of the orifice plates extend over a range of different sizes, a reference pressure transducer arranged to measure the chamber gas pressure, and electronic control means for controlling the progressive operation of the valves in response to the difference between the output from the pressure transducer and a pressure demand signal.

In a preferred embodiment of the invention the manifold has a secondary port or ports connecting the manifold to ambient or low pressure, and the or each of the secondary ports has a fixed orifice plate and a solenoid operated shut-off valve for controlling flow through the port, and wherein the electronic control means controls the operation of the secondary port valve or valves in response to pressure demand signals which are lower than the transducer output pressure signals.

The primary port fixed orifice plates may have flow areas which give flow rates which differ as between plates of a factor of 10.

The smallest of the primary port fixed orifice plates has a flow area which in use gives a pressure drop of less than the desired resolution of the controller over the period of one pressure measurement.

In a further embodiment of the invertion, the controller includes a plurality of reference pressure transducers having different measurement ranges connectable to the manifold via a selector valve, arranged to connect a desired one of the reference transducers.

Embodiments of the invention will now be described by way of example only, with reference to the following schematic drawings of which: Fig. 1 shows a pressure controller in accordance with the invention.

Fig. 2 shows a further pressure controller.

Fig. 3 shows in further detail the controller of Figure 2.

The pressure controller shown in Figure 1 includes a gas pressure regulator 100 which has a high pressure input manifold 1 connected to a gas supply pressure of P,. The manifold 1 is connected to an output manifold 4 by means of five ducts each containing a fixed diameter orifice plate, 1 Oa to 1 Oe, and each duct outlet is controlled by a solenoid operated shut-off valve 2a to 2e. The orifice plates 1 Oa to 1 Oe are of progressively reducing diameter, ratios of the diameter of adjacent plates being chosen to give a flow rate ratio of 1:10. The smallest orifice plate diameter, i.e.: that of plate 1 Oe, is such that a change of pressure of less than the desired resolution of the controller over the time of one pressure measurement is obtained.The output manifold is connected to a chamber 6 which is to be maintained at a desired pressure Pc The output manifold is also connected to a vent duct 5 via orifice plates 1 Of and 1 Og which are controlled by solenoid operated shut-off valves 2f and 2g, respectively.

A pressure transducer 8 is connected via a tube to sense gas pressure Pc in chamber 6.

Output from the transducer 8 and from a pressure selector 7 which produces a signal indicative of desired pressure Ps, is received by a microprocessor unit (mpu) 9, which has outputs on lines 3 which are connected to drive the solenoid valves 2e to 2g. The mpu 9 selects shut-off of one or more of the valves 2a to 2g in response to the difference between the input signals corresponding to Pc and P5. If the desired pressure P5 is lower than Pc then one or both of the valves 2f and 2g are opened to vent the manifold 4 to atmosphere.

Figure 2 shows in schematic form a further pressure controller which includes an input pressure selector manifold 1 5 which is selectively connectable to one of four gas pressure sources P51, Ps2, Pus31 Pus4! covering a range of pressures, and which feeds a gas pressure regulator 1 6 similar to regulator 100 of Figure 1. A transducer selector 1 7 selectively connects one of four pressure transducers 22, 23, 24, 25 to a chamber 11 to sense the gas pressure therein. The transducers 22 to 25 each have a full scale which covers a different part of full range of measurement of the controller.An mpu 26 receives input from a pressure selector 12, similar to the selector 7 of Figure 1 5 and from a selected one of the transducers 22 to 25, and selects shutoff of one or more of the valves of the regulator 1 6 in the same manner as previously described for the regulator 100 of Figure 1. The mpu 26 also controls the selection of the transducers via the transducer selector 17 in accordance with a selected one of the four sources P51 to P54. The pressure controller of Figure 2 permits high resolution measurement over a wide range of pressures, the supply pressure being slightly greater than the full scale of the selected measuring transducer, which allows fine control on low pressure ranges where high resolution is required.

Figure 3 shows the pressure controller of Figure 2 in more detail. A microprocessor and peripheral assembly 36 corresponds to pressure selector 12 and microprocessor unit 26 of Figure 2. Coarsely regulated supply pressures of 20, 60 and 320 psig are supplied to an input pressure selector manifold 47, which corresponds to manifold 15 of Figure 2, via an inlet tube 49 and a second tube 48 connected to a low pressure chamber (not shown) to obtain negative gauge pressures. Three pressure transducers 41, 42 and 43, which have full scale ranges of 4000, 400 and 100 kgPa respectively, are connected to a solenoid valve operated select manifold 44 which corresponds to the selector 1 7 of Figure 2.

The outputs from the transducers are digitized by a digital voltmeter 40. Negative gauge pressures are measured using the reference port of the most sensitive transducer with its measurement port vented. A microprocessor 35 comprising a motorola M6802 with a clock frequency of 1 MH2,controls the selection of the transducers 41, 42, 43 and corresponds to the microprocessor 26 of Figure 2. The microprocessor 35 has the following four interfaces: (i) A keyboard and display interface 34 which provides for manuai control of the pressure source and includes pressure level selection, range change, pressure measurement and zeroing of the transducers 41, 42, 43, and displays commands as entered and, during measurement on regulation displays output pressure in selected units such as, for example psi, kPa or inbars.

(ii) An IEEE bus computer control 33 which provides the same facilities as under (i) above as the keyboard interface and receives digital signals from a remote computer (not shown) via a line 31.

(iii) an IEEE bus digital voltmeter controller 38 is connected to the mpu 35 and the digital voltmeter 40 so as to permit the mpu to read the voltmeter output.

(iv) a valve control and analogue routing interface 37 which connects the mpu 35 via an opto-isolated solenoid valve driver 46 to operate the solenoid valves of the select manifold 44. The valve driver 46 also drives solenoid valves in the selector manifold 47 and a regulation manifold 45 which corresponds to the regulator 1 6 of Figure 2.

The above described apparatus may be used for the simultaneous test of several hundred pressure transducers.

Claims

1. A pressure controller including a manifold for connection to a high pressure gas source, a plurality of primary ports each connecting the manifold to a chamber, wherein each primary port has a fixed orifice plate and a solenoid operated shut-off valve for controlling the flow through the port, and the flow areas of the orifice plates extend over a range of different sizes, a reference pressure transducer arranged to measure the chamber gas pressure, and electronic control means for controlling the progressive operation of the valves in response to the difference between the output from the pressure transducer and a pressure demand signal.

2. A pressure controller as claimed in claim 1 wherein the manifold has a secondary port or ports connecting the manifold to ambient or low pressure, and the or each of the secondary ports has a fixed orifice plate and a solenoid operated shut-off valve for controlling flow through the port, and wherein the electronic control means controls the operation of the secondary port valve or valves in response to pressure demand signals which are lower than the transducer output pressure signals.

3. A pressure controller as claimed in claim 1 or claim 2 wherein the primary port fixed orifice plates may have flow areas which give flow rates which differ as between plates of a factor of 10

4. A pressure controller as claimed in any of the preceding claims further including a selector valve arranged to connect to the manifold a desired one of a set of reference pressure transducers having different measurement ranges.

5. A pressure controller substantially as claimed herein with reference to the drawings.