PRESSURE SENSOR ARRANGEMENT WITH A REMOTELY CONTROLLED ELECTRICAL THRESHOLD DEVICE

Description

[0001] The invention relates to a pressure sensor arrangement with a remotely parameterizable, electrical threshold device having the features of the preamble of claim 1.

[0002] For various technical applications, it is necessary to monitor the prevailing pressure in pressurized systems so that when a limit value is reached, all pressure-generating elements can be switched off via a control system and / or the excess pressure can be reduced in a targeted manner.

[0003] This is particularly true for plastics extrusion systems, where high temperatures regularly occur in the processed plastic melt in addition to high pressures. The relevant standard for plastics extruders, DIN EN 1114-1:2012-01, stipulates in the safety requirements and protective measures that the extruder and other pressurized parts must be protected against exceeding the maximum permissible internal pressure specified by the machine manufacturer. One of the measures considered permissible is the provision of a pressure sensor system according to EN ISO 13849-1:2008, PL = c, which switches off all pressure-generating elements via the control system when a limit value is reached. The latter standard, EN 13849-1:2008, refers to design principles for safety-related parts of control systems and shows the relationship between the required Performance Level (PL) and a Safety Integrity Level (SIL).In this context, there is a requirement that limit values ​​are stored in the overload protection device that cannot be changed during system operation.

[0004] However, the limit values ​​to be specified in the case of plastics extrusion systems are not only system-specific, but may also depend on the material being processed, i.e., they are process-dependent. Consequently, the processor must select suitable sensors, each with different threshold values, from a group of different sensors and install them as required. This entails high costs for the multiple procurement of sensors and the modifications to the system. A pressure sensor arrangement with a remotely parameterizable, electrical threshold device is desirable: the pressure sensor arrangement could be accessed via a data connection, allowing the relevant limit values ​​to be reset using software. This would have the advantage that it can be easily adapted to the specific system in which it is installed and the process carried out there.However, with unsecured, remotely controlled parameterization, it cannot be ruled out that the threshold value device could be accessed via the software level during operation and the limit values ​​could be changed during system operation, potentially resulting in incorrect limit values ​​being stored. Therefore, the firmware and, in particular, external control software would have to be included in the security assessment.

[0005] EP3396347 A1 discloses a pressure sensor arrangement with user-controlled activation from the near field.

[0006] The object of the invention is to further develop a pressure sensor arrangement with a remotely parameterizable, electrical threshold device of the type mentioned above in such a way that a rule-compliant, tamper-proof monitoring of technical systems, in particular pressure monitoring in plastics extrusion systems, is possible.

[0007] This object is achieved by a pressure sensor arrangement having the features of claim 1.

[0008] The invention is based on the fact that the switching thresholds in the pressure sensor array can be changed remotely via an external data line, allowing convenient adaptation to the respective process. However, this requires the physical presence of an operator near the sensor array. The user must open a hardware lock on the internal data bus line between the electronic modules to enable remote access via the external data bus line.

[0009] This provides a solution that, in particular, does not require a safety assessment for software located outside the pressure sensor assembly, such as a machine control system. The invention allows changes to be made by externally controlled software without having to perform a new, complex safety assessment.

[0010] The invention provides for separating the transmission unit from the monitoring unit in such a way that no data exchange is possible between them during operation and thus no access to the monitoring unit can be made from outside the housing. The only data-transmitting connection is essentially physically interrupted by a so-called hardware lock. This is achieved, for example, by routing the data line via a relay. The hardware lock can only be released, and thus the data connection established, if the user acts on a release device inside the housing of the pressure sensor arrangement in the immediate vicinity of the pressure sensor arrangement using physical means that act in the vicinity, in particular means that act or can be used without contact from the outside.

[0011] "Nearby" is therefore defined in the context of the present invention to mean that the release can only be achieved if the user is close enough to the pressure sensor assembly to ensure that a safe operating or idle state exists on the machine in which the pressure sensor assembly is installed before removing the hardware lock.

[0012] In addition to contactless means such as light or electric or magnetic fields, simple mechanical means such as a button accessible from the outside through an opening or a jumper inserted into the housing to release the hardware lock can also be provided.

[0013] The at least one parameterization module for setting the switching thresholds within the monitoring unit is preferably a digital potentiometer.

[0014] Control is preferably via a serial data bus line, and in particular via the Serial Peripheral Interface (SPI) from the microcontroller of the transmission unit. The user accesses the parameterization module from outside the housing via the IO-Link interface.

[0015] The firmware of the transmission unit's microcontroller, as well as the higher-level software layers, are not considered in the security assessment and, according to the invention, do not need to be considered. Therefore, the adjustability of the potentiometer via hardware is disabled once the switching point has been set.

[0016] Optical means can be used for release by using a light-dependent electrical component such as a photodiode, which must be actively illuminated by the user through a housing opening.

[0017] Furthermore, it is possible to use magnetic means to address a reed contact as a release element, or an NFC tag that acts on a suitable reader in the housing.

[0018] The pressure sensor element is preferably connected in parallel to the transmission unit and the monitoring unit, so that the measured value detected by the same sensor element can be transmitted to a higher-level control or regulating device via the transmission unit and a data line such as an IO-Link, and at the same time the measured value can be evaluated in the monitoring unit with regard to the permissible interval.

[0019] The monitoring unit preferably consists of an input amplifier, a comparator with an adjustable switching threshold, and a mechanical or semiconductor relay for the potential-free connection of two terminals, which generates an output signal. While a switching contact is closed when a controlled and permissible operating state exists, the contact is opened in the event of an overload.

[0020] Preferably, the output signal of the comparator is linked to the potential of the supply voltage in the sensor line, so that any disturbances occurring there also cause the contact at the output terminals to open.

[0021] If the voltage supply of the pressure sensor arrangement is interrupted as a whole, the contact is also opened due to the design of the output stage as a normally closed contact.

[0022] A preferred embodiment provides two parameterization modules so that an upper and a lower limit can be set, both of which are monitored by the comparator. While the upper limit directly serves operational safety, monitoring the lower limit serves the purpose of detecting abnormal measured values ​​that may be caused by malfunctions in the pressure sensor arrangement or the system.

[0023] For example, this is the case when the measured pressure appears to be negative. By setting the lower limit to zero, a negative measured value is signaled as incorrect.

[0024] The pressure sensor arrangement according to the invention is preferably designed as a melt pressure sensor arrangement for a plastics extrusion system. This has the special feature that the pressure in the plastics melt must be measured, whereby the pressure sensor arrangement must regularly withstand pressures of more than 100 bar and temperatures of more than 200°C at the measuring point. For this application, a housing with a long, hollow shaft is provided, at the end of which a first membrane is arranged. The membrane is positioned at the measuring point. The actual pressure sensor element is located on another membrane in a housing section beyond the shaft, with the pressure transmission between the membranes taking place via a liquid-filled capillary.

[0025] The process for setting the switching point in the pressure sensor arrangement according to the invention is as follows: The pressure sensor arrangement is connected to an IO-Link master via the provided connections. The mechanical fuse in front of the photodiode, which in a preferred embodiment forms the enable module, is then removed, and the photodiode is illuminated using an external light source such as a flashlight. The parameter for the desired limit value is then written to the respective parameterization module via the IO-Link interface and is thus permanently set in the overload protection device. Once the setting has been completed, the external light source is removed and the mechanical fuse is reattached to the housing opening. Finally, the user must check that the switching threshold has been set correctly by applying the respective signal to the pressure sensor arrangement and moving to the switching point.Once the correct setting of the switching point has been verified, the pressure sensor assembly can be put into operation. If the switching point has not been set correctly, the procedure must be repeated.

[0026] A device is also provided that restores the original state with the internal data bus line interrupted either when a preset time period elapses or as soon as the user ceases to act on the enabling element from close range. The internal data line is interrupted again at the enabling element coupled to the bridge element, so that limit values ​​can no longer be parameterized via the external data bus line.

[0027] The invention will be explained in more detail below with reference to the exemplary embodiment illustrated in the drawings. The figures show in detail: Fig. 1 shows a pressure sensor arrangement in a block diagram; and Fig. 2 shows the housing of the pressure sensor arrangement in section.

[0028] In Figure 1 A block diagram of a pressure sensor arrangement 100 according to the invention is shown. It essentially comprises: a pressure sensor 40, which is constructed in a known form as a bridge sensor according to the Wheatstone bridge principle; a transmission unit 20, which is designed as an IO-Link client and is connected to the pressure sensor 40 via an at least four-pole sensor line 41; a monitoring unit 30; a closed and possibly sealable housing 10, in which at least the transmission unit 20 and the monitoring unit 30 are accommodated.

[0029] The transmission unit 20 and the monitoring unit 30 are housed on a common circuit board 50, but are positioned separately from each other to prevent mutual interference. The two units 20, 30 are connected only by: a common supply voltage supply, which is led from connection terminals 13 on the housing 10 via a multi-core cable 21 to the transmission unit 20 and from there via wires 41.1, 41.3 in the sensor cable 41; the voltage can be provided in particular via an IO-Link master and is 24 V; a parallel connection to the bridge sensor via two wires 41.2, 41.4 in the sensor cable 41; a Serial Peripheral Interface (SPI) 21 for setting the switching threshold, which is connected to the monitoring unit 30 via the data bus line 22.

[0030] The following connections are provided on the housing 10: a two-pin connection 13 for the power supply; an at least one-pin connection 14 for a serial data bus, in particular according to the IO-Link specification, which is routed to the transmission unit 20 via a data bus line 24; an analog output 15, which is connected to an analog line 25, for the optional output of an analog measured value for the measured pressure, and two signal output connections 12, via which, for example, a signal can be output to the outside or an external shutdown device can be actuated.

[0031] Preferably, the pressure sensor arrangement 100 continuously closes a contact between the signal output terminals 12 as long as the values ​​detected by the pressure sensor 40 are within the permissible value range defined within the monitoring unit 30. Conversely, this means that: a failure of the power supply or a failure of components within the pressure sensor arrangement 100 or the exceeding or falling below of the permissible pressure measurement value by the measured actual value each result in the signaling of a safe operating state at the signal output terminals 12 being canceled.

[0032] Also provided on the housing 10 is a recess 11, which can be covered with a translucent cover. Behind it is an enabling module 38, which is designed, for example, in the form of a photodiode or a phototransistor. By temporarily emitting a light beam with a lamp 1 positioned outside the housing 10, an enabling signal is generated at the enabling module 38, which actuates a bridge switching element 32. This closes an internal data bus line 22 of the serial data bus, which was previously permanently interrupted at the bridge switching element 32 and extends from the transmission unit 20 to two parameterization modules 33, 34 in the monitoring unit 30.

[0033] The parameterization modules 33 and 34 are electrical devices for which a characteristic control value can be set via the data bus. These can be, for example, digital potentiometers.

[0034] The upper and lower threshold values ​​for the electrical threshold device 31 implemented in the monitoring unit 30 are stored in the parameterization modules 33, 34.

[0035] The sensor signals from pressure sensor 40 are applied to threshold device 31 via the signal-carrying wires 41.2, 41.4 of sensor line 41. As long as the comparator in threshold device 31 detects that the recorded measured value, possibly after making corrections, is within the permissible range, a positive voltage signal is emitted. This is linked to the positive pole of the supply voltage at pressure sensor 40 via a logical AND gate 35 and wire 41.1. Only when the supply voltage is applied and a positive potential is present at the output of threshold device 31 at the same time does the output of the AND gate also have a positive potential. This actuates a switching element, such as, in particular, an optocoupler 36. Consequently, the contact between terminals 12 is closed, signaling a safe operating state of the machine to which pressure sensor arrangement 100 is attached.

[0036] However, if there is either a voltage drop on the sensor line 41 or if it is detected that the measured and possibly corrected measured value falls below or exceeds one of the threshold values ​​stored in the parameterization modules 33, 34, the potential at the output of the AND gate 35 drops.

[0037] To redefine the threshold values, the activation module 38 must be activated with light. The data bus line 22 is then closed at the bridge switching element 32. Using a data bus line connected from the outside to the transmission unit 20 in the housing 10, each of the parameterization modules 33, 34 can now be addressed one after the other, and a new value can be stored and saved there.

[0038] The light source is then removed from the housing opening 11. The data bus line 22 is interrupted again on the hardware side at the bridge element 32, so that it is no longer possible to access and change the parameterization modules 33, 34 from outside.

[0039] An additional temperature sensor 42 may be provided, which is also connected to the transmission unit 20. Since temperature measurement is not safety-relevant for this application, no switching thresholds need to be parameterized.

[0040] In Figure 2A section through the housing 10 of the pressure sensor arrangement 100 is shown. The housing has a hollow cylindrical housing part 10.1, in which the two essential electronic components, namely the transmission unit 20 and the monitoring unit 30, are housed on the common circuit board 50. A first membrane 43 is arranged at the tip of a hollow housing shaft 10.2. Pressure applied there deflects the membrane 43. A second membrane 44 is deflected via a liquid column located in a capillary line 45. This second membrane 44 is connected to a pressure sensor element 40, so that the conversion into an electrical measurement signal takes place there. Since the electrical measuring sensor is also arranged within the housing, the housing can be completely closed.

[0041] The connections 12, 13, 14, and 15 are combined in a multi-pin plug or a multi-pin socket on an upper housing part 10.3, which closes off the hollow cylindrical housing part 10.1. A closable housing opening 11 is provided in the cover-like housing part 10.3 to illuminate the optically active release element 38 mounted inside the circuit board 50. After the pressure sensor arrangement 100 has been parameterized, the housing opening 11 is closed, e.g., with a screw, preventing the illumination of the release element 38. Reference symbols:

[0042] 100Pressure sensor arrangement 10 Housing 10.1, 10.3 Housing parts 10.2 Housing shaft 11 Housing opening 12 Connection terminals 13 Power supply connections 14 Connection for external serial data bus 15 Analog output 20Transmission unit 21Serial Peripheral Interface 22Internal data bus line 23Power supply line 24Data bus line 25Analog value line 30Monitoring unit 31Threshold device 32Bridge switching element 33, 34Parameterization modules 35AND gate 36Optocoupler 38Release element 40Pressure sensor element 41Sensor cable 41.12...41.4Wires of the sensor cable 42Temperature sensor 43First membrane 44Second membrane 45Capillary line 50 boards 1 light

Claims

1. Pressure sensor assembly (100) having a remotely parameterizable, electrical threshold device (31), at least comprising: - an electrical sensor element (40); - a transmission unit (20) which is connected at least to the sensor element (40) and to a data bus line (24) leading to an external connection (14); - a monitoring unit (30) which contains the threshold device (31) and is connected to the sensor element (40) and an actuator for generating an output signal; - a closed housing (10) in which at least the transmission unit (20) and the overload protection unit (30) are arranged; characterized - in that the transmission unit (20) is connected to the monitoring unit (30) via at least one internal data bus line (22) which is interrupted at an electrically switchable bridge switching element (32), and - in that at least one parameterization module (33, 34) connected to the threshold device (31) is provided in the monitoring unit (30) for adjusting a lower and / or an upper pressure limit value, which parameterization module can be connected to the transmission unit (20) via the internal data bus line (22) by closing the bridge switching element (32), and - in that the bridge switching element (32) can be closed via a release element (38) which can be actuated out of the region close to the housing (10) from the outside.

2. Pressure sensor assembly (100) according to Claim 1, characterized in that the parameterization module (33, 34) is designed as a digital potentiometer which is connected to the internal data bus line (22).

3. Pressure sensor assembly (100) according to Claim 1 or 2, characterized in that a respective parameterization module (33, 34) is provided for a lower and an upper limit value and both parameterization modules (33, 34) are connected to the threshold device (31).

4. Pressure sensor assembly (100) according to any of the preceding claims, characterized in that an output signal of the threshold device (31) is connected to the potential of the supply voltage in the sensor line (41) via an AND element (35).

5. Pressure sensor assembly (100) according to Claim 4, characterized in that the output signal of the threshold device (31) or the AND member (35) is applied to an optocoupler (36) or to a relay by which two signal output connections (12) can be connected to each other without potential.

6. Pressure sensor assembly (100) according to any of the preceding claims, characterized in that the release element (38) is an optically acting electrical element, and in that the housing (10) has at least one closable housing opening (11) by means of which the release element (38) can be illuminated.

7. Pressure sensor assembly (100) according to any of the preceding claims, characterized in that the release element (38) is a magnetically acting, electrical element.

8. Pressure sensor assembly (100) according to any of the preceding claims, characterized in that the sensor element (40) is a pressure sensor element for a plastic extrusion system and the pressure is transmitted via a liquid column in a capillary line (45) between a first membrane (43) at the tip of a housing shaft (10.2) and a second membrane (44) which is connected to the pressure sensor element (40).

9. Method for adjusting a switching point in a pressure sensor assembly (100) having a remotely parameterizable, electrical threshold device (31) according to any of the preceding claims, comprising at least the following steps: - connecting the pressure sensor assembly (100) to an external data bus line; - closing the internal data bus line (22) by means of the bridge switching element (32) by user action on the release element (38) from the region close to the pressure sensor assembly (100) and from outside the housing (10); - writing at least one parameter for a limit value to the parameterization module (33, 34) via the external data bus line (22) and - disconnecting the internal data bus line (22) by terminating the action on the release element (38).