Valves and valve actuation – Electrically actuated valve – Remote or follow-up control system for electrical actuator
Patent
1996-06-21
1998-01-06
Ferensic, Denise L.
Valves and valve actuation
Electrically actuated valve
Remote or follow-up control system for electrical actuator
137554, 13712901, F16K 3102
Patent
active
057045860
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for controlling a valve between a number of fixed positions of the type which comprises a magnetic valve which supplies an amount of fluid to a pressure cylinder which activates the valve.
In chemical industry it is usual to activate valves by means of pneumatic or hydraulic cylinders which are controlled by magnetic valves. Within certain industries there is a requirement for monitoring signals to allow determining that the valve has moved mechanically to the desired position so that it is either open or closed or has a desired position between these extremes. These signals are typically generated by microswitches which may be fitted so that they have a well-defined position at closed, open, or the desired position therebetween. In the case that a monitoring signal has to be given for "fully open" and "fully closed" two microswitches are used. Inductive sensors, possibly of the on/off type, may also be used. The purpose of the monitoring is to create a certainty that the valve has indeed been activated to the desired position. The requirement for the precision of the valve position may be in the order of magnitude of 0.1 mm, in particular if the system is also supposed to catch faults in the valve seat gasket or a totally missing valve seat gasket.
The present system is very difficult and time-consuming to adjust, since it consists in moving to or several microswitches upon activation to each position. Wear of the valve and the valve seat gasket require frequent adjustment. The mechanical construction requires instrument quality adjustment facilities. Valves which operate at changing temperatures similarly need different adjustments dependent on temperature, and in particular this problem has been difficult to solve until now.
It is the purpose of the invention to provide an apparatus which solves the desired tasks without the disadvantages mentioned. This is obtained in an apparatus according to the invention which is particular in that the valve stem is provided with a linear position indicator which gives a series of readings during the movement of the valve stem, of which the readings relating to the desired fixed position are stored in a data store during a first activation of the valve, whereby the result of subsequent activations of the valve is determined by comparing the instant reading with a stored reading for a desired fixed position. A position indicator may be e.g. of the type difference transformer which is non-contacting, or optical which is based on optically reading a coded rod. Thereby, instead of a manual adjustment of microswitches it is a question of determining position data corresponding to the desired positions and storing them as a future reference. Thus it is possible to let a calculating unit place an uncertainty interval around the position indication to be obtained, and similarly the determination of slow changes in the position indication for the fixed points developed during many activations of the valve in question may enable automatic compensation for wear and/or settling of the valve seat gasket. One may actually perform a statistical analysis of the position indication relating to the extreme position obtained, in order that slow drift is compensated or accepted while a sudden change causes an alarm. Furthermore the whole data stream of position indications can be monitored during an activation, in that a certain time is provided for the change from one position to another, and an instant report may be had in case the valve is not activated in a regular fashion.
Similarly it becomes possible to compensate by calculation the influence of temperature on the dimensions of the valve, in case the position monitor is fitted together with a temperature sensor.
In practice the whole monitoring system is cast into an insulating and sealing compound, and in this case one will use a non-contacting system. In this manner a very stable construction is obtained which has a much higher probability of error-free survival in the frequently aggressiv
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Ferensic Denise L.
Kim Joanne
Safran David S.
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