Residual pressure sensor and residual pressure sensor monitoring

Details Residual pressure sensor and residual pressure sensor monitoring Residual pressure sensor and residual pressure sensor monitoring

1996-01-29

1997-10-07

Crosland, Donnie L.

Communications: electrical

Condition responsive indicating system

With particular system function

340555, 340626, 73705, 73732, 73733, G08B 2900, G01L 900

Patent

active

056753179

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a residual pressure sensor which uses a Bourdon tube to detect a drop in pressure. In particular the invention relates to a residual pressure sensor which is suitable for guard systems such as those covered under Chapter 9 of British Standard BS 5304, for fail-safe verification of stoppage of drive power to hydraulically powered machinery. Moreover, the present invention relates to a residual pressure sensor monitoring apparatus for monitoring if a residual pressure sensor is normal or abnormal.


BACKGROUND ART

In cases for example wherein maintenance work is carried out with a movable section of a machine in a holding condition, or with operations wherein a movable section of the machine and an operator co-operate alternately, safety measures to protect the operator from accidents are extremely important. In the case of hydraulically powered machinery for example, safety measures can be taken involving a method wherein an operator is permitted to approach close to a movable section of a machine only after verifying that the pressure source has been cut off and that pressure is not being supplied to the movable section of the machine. In this case, a safety system can be considered wherein the presence or absence of a pressure supply to the movable section of the machine is monitored for example by a residual pressure sensor, and the operator is warned by the display of a lamp or the like.
As a pressure detection sensor suitable for such types of safety systems, there is the residual pressure sensor previously proposed by the present inventors in Japanese Unexamined Patent Publication No. 6-307952.
This residual pressure sensor has a pressure sensing pipe (Bourdon tube) bent into an approximate C-shape, with a closed end, which is displaced in proportion to the introduced pressure, provided with a plate having a slit. Moreover, the construction involves a photocoupler comprising mutually opposed light emitting and light receiving elements arranged with the plate therebetween, with an output from the photocoupler and clamped at a power source voltage and rectified by means of a voltage doubler rectifying circuit.
In operation, the pressure sensing pipe is communicatively connected to a pressure supply pipe for supplying pressure from a pressure source to a movable section of a machine. In this condition, when there is no pressure in the pressure supply pipe so that the pressure introduced to the pressure sensing pipe is practically zero, the closed end of the pressure sensing pipe is not displaced, and an alternating current light beam from a light emitting element which is driven by an alternating current signal from a signal generator, is received by the light receiving element via the slit of the plate. As a result, an alternating current output is generated from the photocoupler, so that an electrical output signal of a higher level condition (logic value "1") than the power source voltage, is generated from the voltage doubler rectifying circuit, and a display lamp illuminated to indicate no pressure (movable section of the machine stopped).
On the other hand, when there is a pressure supply to the movable section of the machine so that the movable section of the machine is in a drive condition, pressure is also introduced into the pressure sensing pipe, displacing the closed end thereof in proportion to the introduced pressure. Due to this closed end displacement, the plate is also displaced, shutting off the light beam projected from the light emitting element towards the light receiving element. As a result, an alternating current output signal is not generated from the photocoupler, and hence the output of a higher level than the power source voltage is not generated from the voltage doubler rectifying circuit (the rectifying circuit output becomes a low level condition of logic value "0"), so that the display lamp does not come on, thus indicating a pressure (movable section of the machine movable).
With this residual pressure sensor, since at th

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