GB2248776A - Testing of pressure detectors - Google Patents

Abstract

The invention relates to a process and a device for the operational test of a membrane-resistance and/or piezo- resistive pressure detector. Detectors installed in explosion-endangered installations must be examined for operability using the process and device. By means of the process in accordance with the invention equalized compressed air or compressed gas is regulated to a desired value and then the pressure detector is loaded with this test pressure. Desired value and test pressure are displayed separately, whereby the associated switch point can be read optically and/or acoustically. The devices required for carrying out the process are accommodated in a carrying case.

Description

1 224377o Process and device for the operational test of

membrane-resistive and/or piezo-resistive pressure detectors The invention relates to a process and a device for the operational test of a membrane-resistive and/or piezo-resistive pressure detector, which is used in explosion-endangered installations in connection with an explosion-suppression installation having a control and monitoring unit, whereby the pressure detector, registering at least one explosion-typical characteristic quantity, is loaded in the dismantled state with compressed air and the test pressure is compared with the set characteristic quantity.

Processes and devices of this kind serve the safety of and thus the constant readiness of the explosion-suppression installations. These are applied to containers. production systems or suchlike, in which, through the processing, transport and storage of explosive gases and powders, a considerable risk of explosion and fire arises. The explosion-suppression installations serve to avert danger and in particular to suppress incident explosions.

An explosion-suppression installation consists, for example with a container filled with explosive gases, of a pressure detector and one or several containers for extinguishing agents, which are attached to the outer side of the container and are connected to the inside of the container by means of openings. The pressure detector is connected by means of electrical lines to a control and monitoring centre to current supply. Likewise, the containers for extinguishing agents are connected by means of electrical lines to the control and monitoring centre. The containers for extinguishing agents are provided with valves which can be controlled pyrotechnically, the valves opening extremely quickly. With an incident gas or powder explosion a pressure wave rushes out of the flame front, the pressure wave amounting to a multiple of the velocity of sound. The pressure wave can be recognized by a suitable pressure detector.

If the pressure detector recognizes a pressure wave, the latter is then supplied to the control and monitoring centre with very fast signal evaluation, so that the valves of the containers for extinguishing agents open abruptly. The extinguishing agents are distributed homogeneously very quickly within the container and the running flame front i thus extinguished by means of the so-called anti- catalytic effect. An explosion and thus the destruction of the container is avoided.

A prerequisite for the sure function of an explosion-suppression installation is a pressure detector, operating absolutely reliably, which registers an explosion-typical and/or operational characteristic quantity. Through incrustations, cakings or other harmful influences the response time of the detector can be delayed or prevented. In such a case a sure explosion suppression is no longer guaranteed. For operational testing, membrane detectors have hitherto been loaded with low pressure from the outside. Such a test, however, is inaccurate and, in addition to this, also illegal. The detectors have also been dismantled and loaded with pressure by means of an appropriate device. The switch point was recorded by an ohmmeter, an inspection light or a buzzer. In explosion-endangered spaces an ordinary ohmmeter is not admissible unless it is appropriately encased.

The object of the invention is to create a process and a device, with which pressure detectors can -3 be manually examined for their operability without electrically operated components at previously determined intervals on site in explosion- endangered spaces.

This object is achieved in that the compressed air is buffered or equalized, regulated to a desired value and then the pressure detector is loaded with a test pressure, whereby the regulated desired value is displayed on a first pressure gauge and the test pressure is displayed on a second pressure gauge and the associated switch point is read or listened to optically and/or acoustically on a further apparatus.

With this process the pressure and thus the switch point of the detector which is to be examined is can be regulated accurately. If this pressure corresponds with the test pressure, the detector to be tested is loaded or pressurized. Its operability is thereby demonstrated. The loading of the pressure detector can also take place in that it is loaded or pressurized with the test pressure by means of a fast acting opening. This means that the pressure passage to the detector remains closed until the desired value is regulated accurately. In this way it is ensured that the detector is actually loaded or pressurized with the test pressure.

The containers to be protected are frequently filled with a medium which is under pressure, whereby the change of this pressure is displayed in the control and monitoring centre. With the operational test it can be ascertained whether the detector for this region has the appropriate switch point.

Due to outer influences, for example extreme heat in midsummer, the contents of the container to be protected can warm up, whereby the inner pressure increases. This pressure only increases slowly. The detector, however, should only display an explosion- typical characteristic quantity, which corresponds with a pressure increase within a certain time, thus for example with a pressure increase within a time such as 0.3 seconds on a set pressure degree for example from 60 to 160 mbar. If the inner pressure of the container increases slowly to this higher pressure, the extinguishing installation is not put into operation.

The detector can be set in such a way that it recognizes another further characteristic quantity, for example a maximum pressure. If the pressure increases slowly due to outer influences, therefore not through explosion, then the detector must respond at a previously determined maximum pressure. This characteristic quantity can also be examined by the process in accordance with the invention.

In this way the following characteristic quantities can be tested: The characteristic quantity of an altered operational pressure; 2. the explosion-typical characteristic quantity with a pressure increase within a predetermined time unit; the maximum characteristic quantity, at which the pressure detector responds in all cases.

After the end of the operational test the compressed air can be conducted to the outside.

An advantageous device for carrying out the process is seen in that the equipment required for the operational test is accommodated with the associated lines and connections within a case. With a carrying case of this kind a monitoring inspector can examine easily and absolutely safely the operability of pressure detectors at the works.

The process is described in more detail with the aid of a circuit diagram and the device is 3.

described in more detail with the aid of an exemplary embodiment. These are represented in a drawing.

Figure 1 shows a circuit diagram.

Figure 2 shows the inner view of an opened carrying case with a top view of a front plate.

Figure 3 shows the opened carrying case with a view of the rear side of the front plate.

Figure 4 shows a hand pump.

The process in accordance with the invention is described in more detail first of all with the aid of Figure 1. To a connector 1 there is attached a pressure generator P which can consist of a hand pump, a gas bottle or of a fixed compressed-air line with attachment hose. From the connector 1 a line 2 leads to a back-up container 3, in which a certain quantity of compressed gas is stocked. From the back-up container 3 a line 4 leads to a regulator 5, with which the desired value to be examined can be accurately regulated. By means of a line 7 the desired value can be displayed on a first pressure gauge Pl. From a junction 6 a line 8 leads to a fast-acting switch 9, from which a line 10 leads to a junction 11. From here a further line 12 leads to a second pressure gauge P2. A line 13 with a three-way valve 14 and a line 15 for a receiving body 16 is provided for receiving different pressure detectors. The three-way valve 14 is constantly open during the operational test in the passage from the line 13 to the line 15. Only the passage to the junction 14a is closed. By means of the line 14a the compressed air can be conducted to the outside after the end of the operational test. The fast- acting switch 9 can be closed or open during the operational test. With the fast-acting switch 9 open the test pressure is slowly regulated so that the pressure detector, as desired, is thereby loaded. More advantageous is the regulation with the fast-acting switch 9 closed, which must be constructed as a fast switch for this case. Due to the quantity of air supply within the back-up container 3, by means of the regulator 5 with the fast-acting switch 9 closed the desired value can be regulated accurately as very fine regulation. If the desired value is achieved, the fast-acting switch 9 is opened abruptly so that the detector to be tested is loaded with the desired test pressure.

In explosion-suppression installations both membrane pressure detectors 31 or piezo-resistive pressure detectors 34 can be used. With the process in accordance with the invention both pressure detectors can be tested. For this purpose, the receiving body 16 is provided with a device 16a which is led by means of an opening 33 in a floor plate 32 of the detector to the detector. Alternatively, the receiving body 16 can be provided with a device 16b which leads to a connecting piece 35 of the detector 34. The pressure detector 31 is provided with a connector 31a and the pressure detector 34 with a connector 34a. Electrical cables 39 and 40 can be attached to these connectors and conducted further for example to a fire-signalling centre 37, which in most cases belongs to an explosion suppression installation. Alternatively, the electrical cable 40 can be attached by means of a further electrical cable 41 to an ohmmeter 38, an inspection light or a buzzer.

The apparatus lines and connections necessary for the operational test can be accommodated without difficulty in a carrying case 18, which is represented in Figures 2 and 3. Figure 2 shows the opened carrying case 18, consisting of a case housing 19 and a cover 20. Within the carrying case mountings 21 are attached in the upper part of the case housing 19 (see Figure 3), on which mountings a front plate 23 is placed and by means of connection elements 24 can be connected in a releasable manner. To the front plate 23 there are connected the two pressure gauges P1 and P2 as well as the connector 1 for the pressure generator 27 of the regulators 5, the two switches 9 and 14 as well as the receiving body 16. The receiving body 16 has a receiving plate with an opening 16a. The latter is provided for the examination of the pressure detector 31. After dismantling from the explosion-endangered installation, the pressure detector 31 is mounted on to the receiving plate and is fastened by means of fastacting clamps 26 in a tight and sealed manner. In this assembly state the pressure detector can be loaded with compressed air. With the use of a piezo- resistive pressure detector 34 the latter is screwed with its connecting piece 35 into the threaded bore 16b of the receiving plate. It is connected absolutely tightly to the receiving body 16 and can therefore be loaded in this assembly state likewise with compressed air. The receiving body 16 is fastened by means of a fastening plate 17 and fastening elements 25 to the underside of the front plate 23 (see Figure 3 in this respect). The fastening of the connector 1 is denoted as la, the fastening of the switch 9 as 9a and the fastening of the switch 14 as 14a. 5a shows the underside and fastening of the regulator 5. The two pressure gauges P1 and P2 are also guided through the front plate 23 and fastened on the underside with it. On the floor 22 of the carrying case 18 the back-up container 3 is fastened by means of devices 3a. The holding devices 21 are arranged in such a way that the front plate 23 can be built into the carrying case, without touching the back-up container 3. Figure 3 shows the individual lines, with which the equipment is connected for the execution of the process in accordance with the invention. Thus, the line 2 is guided from the fastening la of the connector 1 to the back-up container 3. From there the line 4 goes to the fastening Sa of the regulator 5, from which a line 7 leads to the pressure gauge Pl. From the junction 6 a line 8 goes to the fastening 9a of the switch 9, from which in turn the line 10 leads to the junction 11. From this junction 11 on the one hand the line 12 goes to the pressure gauge P2 and on the other hand the line 13 goes to the fastening 14a of the switch 14. From there a line 15 goes to the receiving body 16.

Figure 4 shows a hand pump 27 with a connector 29, a pump body 28 and rubber bellows 30. The attachment 29 can be inserted into the connector 1. Both parts are constructed as a quick coupling. The hand pump 27 can be accommodated in the cover 20 so that the examining inspector has a pressure generator at his disposal at all times and is therefore not dependent on pressure generators at the buildings.

claims 1. Process for the operational test of a membrane-resistive and/or piezo- resistive pressure detector, which is used in explosion-endangered installations in connection with an explosionsuppression installation having a control and monitoring unit, whereby the pressure detector, registering an explosion-typical or other characteristic quantity, is loaded in the dismantled state with compressed air and the test pressure is compared with the set characteristic quantity, characterized in that the compressed air or a compressed gas is equalized, regulated to a desired value and then the pressure detector is loaded with a test pressure, whereby the regulated desired value is displayed on a first pressure gauge and the test pressure is displayed on a second pressure gauge and the associated switch point of the pressure detector is read or listened to optically and/or acoustically on a further apparatus.

2. Process according to claim 1, characterized in that the pressure detector is loaded with the test pressure by means of a fast-acting opening.

3. Process according to claims 1 and 2, characterized in that the compressed air is conducted to the outside after the end of the operational test.

4. Process according to claims 1 to 3, characterized in that several operational tests are carried out one after the other.

5. Process according to claim 4, characterized by the testing of the following characteristic quantities:

a) the characteristic quantity of an altered operational pressure of the explosionendangered installation; b) the explosion-typical characteristic quantity with a pressure increase within a predetermined time unit; the maximum characteristic quantity, with which the pressure detector must respond in all cases. 6. Device for carrying out the process according to claims 1 to 5, characterized in that the equipment required for the operational.test, such as connector, back-up container, regulator, switches, pressure gauges and the associated lines is accommodated within a carrying case.

7. Device according to claim 6, characterized in that the carrying case is provided is with mountings for fastening a front plate, with which the equipment is connected, whereby the back-up container is fastened underneath the front plate to the floor of the carrying case.

8. Device according to claims 6 and 7, characterized in that the front plate is provided on the underside with a fastening plate, to which there is fastened a receiving body for receiving the pressure detector.

9. Device according to claim 8, characterized in that the receiving body on the upper side of the front plate has a receiving plate, which is provided with an opening for the pressure loading of a membrane pressure detector and with a threaded bore for screwing in a piezo-resistive pressure detector.

10. Device according to claims 6 to 9, characterized in that on the upper side of the front plate fast-acting clamps are associated with the receiving body for fastening the membrane pressure detector.

11. Device according to claims 6 to 10, characterized in that the carrying case contains a hand 1 pump, which is fastened in a releasable manner in the cover and has a quick-coupling piece, which can be inserted into the connector.

12. Device according to claims 6 to 11, characterized in that the lines are fastened to the underside of the front plate.