The term “position regulator” used in this disclosure represents a mechatronic system which controls auxiliary energy of an actuating drive, such as a pneumatic actuating drive, on the basis of one or more input signals in order to move the valve element to a specific position. In order to operate, the position regulator can use pressurized gas (e.g., compressed air) as auxiliary energy, and electrical energy as well.
Pneumatic position regulators are known which operate a process valve. With a pneumatic system, the drive chambers of a single-acting or double-acting pneumatic actuating drive are ventilated or vented deliberately as a function of one or more input signals. The pneumatic system can include an auxiliary energy supply line, one or more pilot valve arrangements and control pressure supply lines to the drive chambers in order to control the ventilation and/or venting of the drive chambers. The movements and positions of the valve element can be represented as one or more signals with the aid of a position sensor as a position feedback sensor system. Furthermore, a control electronics system can be provided which has a microcontroller and receives one or more input signals. The firmware in the control electronics processes the input signals and the signals from the position sensor system to form output signals which are used as input signals for the pneumatic system.
The firmware on the position regulator implements a function which analyzes the dynamic characteristics of the enclosed pneumatic actuating drive. During startup, the actuating range of the valve element is moved through once during an initialization process, and an initial value and final value of the actuating range are recorded.
Actuating operations are subdivided into pivoting drives and linear-movement drives. In the case of a linear-movement drive, the linear movement of the output drive of the actuating drive is transmitted directly to a linearly operating actuating member. In contrast, in the case of a pivoting drive, the linear movement of the output drive of the actuating drive is converted to a rotary movement by suitable device (e.g., mechanical linkage).
The pneumatic actuating drive and the position regulation are linked by a fitting kit. The fitting kit can include components which transmit the movement and position of the actuating drive with respect to the position feedback sensor system to the positioning regulator.
During operation of process valves for the purposes stated above, an unpredicted failure of a single valve can adversely affect an entire production installation or the like. In the extreme, this can lead to a total shutdown. In order to cope with this, attempts have already been made to carry out preventative replacement after an estimated life of the valve mechanism has elapsed. In this method, the replacement was, however, frequently carried out even well before the actual wear limit, since there is a wide scatter between the estimated life and the actual life.
EP 0 739 503 B1 discloses a valve arrangement having a position regulator which also has a diagnosis device for operating state monitoring. The positioning regulator of the valve element, which in this case is in the form of a closure body for a valve seat, operates on the basis of an electrical actuating signal which is predetermined externally. An appropriate sensor system within the positioning regulator measures the current disturbance of the valve element and the control pressure to and from the drive chambers is influenced in order to move the valve element to the desired position. The control pressure is provided by an external control pressure shaft and is supplied to the drive chamber from an internal pilot valve arrangement, depending on the actuating signal, or the drive chamber is vented in order to move the valve element in the correct direction. In this case, the movement is carried out by an integrated resetting spring.
Because component dimensions can be quite small and the switching frequencies can be quite high, the valve mechanism of a pilot valve arrangement can be particularly sensitive to dirt which causes wear and which can be transported in particular by the compressed air in the area of the sensitive pilot valve arrangement. A failure of the pilot valve arrangement can lead to a defect in the pneumatic system, which can result in the entire valve arrangement being shut down. In addition to dirt, leakages should be avoided, in particular in the area of the pneumatic lines between the pneumatic valve and the connected actuator.
WO 2005/109140 A1 discloses an electronic evaluation unit for monitoring the operating state of a valve arrangement. The pressure in front of and behind the valve element of a pneumatic valve is measured for this purpose. Furthermore, the opening cross section of the valve element is determined by a position sensor system. The gas flow rate through the pilot valve is calculated using this data. Conclusions about the operating state of the pneumatic valve can be drawn by analysis of the gas flow rate in actual operating conditions. It is thus possible to obtain indications of a normal operating state or of a fault state, in order to take maintenance measures in good time.
This electronic evaluation unit for diagnosis of the operating state involves a sensor complexity which can be quite high. This is because different pressure sensors and additional sensors are used and undetailed information is made available about the pneumatic system in order to make it possible to detect a malfunction in the system.
In other known systems, the control pressure acting on a valve element can be determined and evaluated by sensors in order to determine the sliding friction during the movement of the valve element. Since the control pressure is proportional to the drive force of the valve element if the control piston diameter is constant, it is possible to use the measured pressure value to determine the drive force required to move the valve element. If the drive force increases over the course of the operating time of the pneumatic valve, then this can be an indication of increasing wear.