Improvements in or relating to field equipment

Abstract

The present invention provides a method for verifying the functioning of a liquid level detection device, preferably a vibrating tuning fork liquid level switch, while the device remains in place. The method includes verifying, independently of the device, whether the tines of the tuning fork are completely wet or completely dry. This step can be performed using a separate, independent liquid level measurement device.

Description

Technical Field

[0001] The present invention relates to liquid level switches used in process control, and in particular to methods and / or systems for verifying the state of such switches when in situ in an operational environment. Although the following description is directed to a vibrating tuning fork liquid level switch, those skilled in the art will appreciate that the methods disclosed herein may also be applied to other liquid level switch technologies, including but not necessarily limited to capacitance and vibrating rod. Background Art

[0002] The vibrating tuning fork level switch is a well-known device used extensively in process control applications. Typically, the device is driven at its resonant frequency, which varies depending on the medium in contact with the tuning fork's tines. In a typical application, the tuning fork is mounted on the wall of a tank into which liquid is pumped, with the tines protruding into the tank's interior. As long as the tines remain uncovered, the tines vibrate at a "dry" frequency, but when the liquid level in the tank rises to cover the tines, the tines vibrate at a lower "wet" frequency. These changes in the tuning fork's frequency are monitored, and when the frequency changes from dry to wet, the instrument initiates a switching action—for example, starting or stopping a pump, or triggering a high-level alarm or warning.

[0003] In another application, the instrument can be mounted near a low liquid level or at the base of a tank, where the tines would normally be covered by the process liquid. In this application, when the liquid level drops below the tines, the frequency will rise from the wetted frequency to the dry frequency. This change could, for example, start or stop a pump or trigger a low-level alarm or warning.

[0004] Typically, the operation of a switch will vary over time, so it is important to verify the health of the switch and ensure it is operating within acceptable parameters. For example, over time, the tines may become coated with residue from the process fluid in contact with the switch, or the tines may corrode; both of which will change the wetting and drying frequencies.

[0005] Historically, this type of switch would be inspected by a field engineer, who would note the switch's location, manually disassemble it, and physically inspect it. This process is time-consuming and costly from a labor perspective, and often requires interruption / shutdown of the process. Furthermore, engineers could be exposed to risks if exposed to toxic process fluids / vapors, or working at height in the case of switches mounted on top of tall tanks.

[0006] In our International Patent Application No. WO 2010 / 055415, we described a method for detecting coatings on tuning fork tines without requiring physical contact with the instrument. However, the method described assumed that if the observed sensor frequency was within a certain frequency band, the sensor was either wet or dry, as the case may be. The problem with this assumption is that dry process material can bridge the space between the tines, resulting in a frequency that indicates wetness, when the tines are actually in a dry space above the liquid surface.

[0007] It is an object of the present invention to provide a method and / or system for verifying the operating condition of a liquid level transmitting device which solves the above problems at least to some extent; or at least provides a novel and useful option. Summary of the Invention

[0008] Thus, in a first aspect, the present invention provides a method of monitoring the condition of an apparatus configured to determine the level of a liquid in a container, the method comprising the steps of: providing at least one reference value of an operating parameter, the at least one reference value indicating whether the apparatus is completely above the liquid ("dry") or completely immersed in the liquid ("wet"); obtaining, by the apparatus, a current value of the operating parameter; determining, independently of the apparatus, whether the apparatus is wet or dry when the current value of the operating parameter is obtained; comparing the current value of the operating parameter with at least one reference value of the operating parameter; and providing an output indicative of the condition of the apparatus based on the comparison and the determination of whether the apparatus is wet or dry.

[0009] Preferably, the method comprises comparing the observed operating parameter with stored operating parameters within a given range.

[0010] Preferably, the device is a vibrating tuning fork liquid level switch configured to operate in resonance; the at least one predetermined stored operating parameter comprises a resonant frequency range of the vibrating tuning fork liquid level switch when dry and when wet, respectively; and wherein the observed operating parameter is the resonant frequency.

[0011] The step of verifying whether the device is wet or dry may be manually established and manually input to the device through a local operator interface or through a command via a communication protocol.

[0012] Alternatively, the step of verifying whether the device is wet or dry is performed using a further independent level detection device, the device and the further level detection device communicating automatically via a common communication protocol.

[0013] Preferably, the method comprises the use of an additional independent continuous level measurement device.

[0014] Preferably, a plurality of level sensing devices are comprised in a circuit with said further level detection means communicating with all of said devices via a common communication protocol.

[0015] Preferably, communication is effected via HART or Fieldbus protocols.

[0016] Preferably, the stored operating parameters indicative of drying are set by a drying calibration procedure.

[0017] Preferably, the dry calibration procedure includes adaptation to frequency variations due to temperature and / or pressure.

[0018] Preferably, the stored parameter indicative of wetting is set when the device is mounted on the container; or by exposure to a sample of the process liquid prior to mounting.

[0019] Preferably, the step of providing an output indicative of the condition of the device comprises transmitting an output of "OK", "Caution" or "Alarm".

[0020] Preferably, said observed operating parameters and subsequent changes in said observed parameters are stored within said device, said method comprising determining from said changes one or more trends indicative of physical changes in said device.

[0021] In a second aspect, the present invention provides a level sensing device for determining the level of a liquid in a container, the level sensing device comprising: a memory for storing at least one reference value of an operating parameter, the at least one reference value indicating whether the device is completely above the liquid ("dry") or completely immersed in the liquid ("wet"); an actuator configured to exhibit different values ​​of the operating parameter depending on whether the actuator is wet or dry; and a processor coupled to the actuator and configured to: obtain a current value of the operating parameter from the actuator; receive a result of a determination, performed independently of the device, of whether the device is wet or dry when the current value of the operating parameter is obtained; compare the current value of the operating parameter with at least one reference value of the operating parameter stored in the memory; and provide an output indicating a condition of the device based on the comparison and the result of the determination of whether the device is wet or dry.

[0022] Preferably, the liquid level sensing device comprises a vibrating tuning fork liquid level switch.

[0023] In a third aspect, the present invention provides a monitoring system for monitoring the condition of a container, comprising: a liquid level sensing device for determining the liquid level of a liquid in the container, the liquid level sensing device including an actuator, the actuator being configured to exhibit different values ​​of an operating parameter depending on whether the actuator is wet or dry; and a processor coupled to the actuator and configured to obtain a current value of the operating parameter from the actuator; and a host system that communicates with the liquid level sensing device, the host system including processing circuitry configured to: receive the current value of the operating parameter from the liquid level sensing device; compare the current value of the operating parameter with a reference value of the operating parameter indicating whether the liquid level sensing device is completely above the liquid ("dry") or completely immersed in the liquid ("wet"); and provide an output indicating the condition of the device based on the comparison and a determination performed independently of the liquid level sensing device whether the liquid level sensing device is wet or dry when the current value of the operating parameter is obtained by the processor of the liquid level sensing device.

[0024] After reading the following description, those skilled in the art will be able to make many variations to the embodiments of the present invention. The following description should not be considered limiting, but merely as an illustration of one way to implement the present invention. Within the scope of the appended claims, whenever possible, any element or component should be deemed to include any and all equivalents thereof, whether or not specifically mentioned. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0026] Figure 1 : shows a schematic diagram of a monitoring system according to an embodiment of the present invention;

[0027] Figure 2 : shows a diagram of a dry tuning fork frequency band in which the frequency varies with process temperature;

[0028] Figure 3 : a diagram showing a dry tuning fork frequency band in which the frequency varies with process pressure; and

[0029] Figure 4 : Graph showing the frequency of a wetted tuning fork in different liquids where the frequency varies with the density of the process liquid. DETAILED DESCRIPTION

[0030] The present invention provides a method and system for verifying the operating condition of a device for indicating the level of a liquid medium in a container (e.g., a process tank). Although the present invention can be applied to such devices operating according to a variety of different technologies, the examples in this detailed description relate to a vibrating tuning fork liquid level switch.

[0031] Figure 1 Schematically shown is a monitoring system 1 for monitoring the status of a container 5 (including a first vibrating liquid level tuning fork switch 6 and a second vibrating liquid level tuning fork switch 7), and a host system 3 shown as a control room.

[0032] like Figure 1 As shown, vibrating fork level switches 6 and 7 are mounted on the wall of a process tank or vessel 5. Tank 5 contains process liquid 8, the upper surface of which is shown at 9. By way of example only, switches 6 and 7 may include those sold under the trademark Rosemount 2140.

[0033] Switch 6 is a high-level switch. That is, it is typically uncovered or "dry," and performs a switching function or outputs an alarm when the liquid surface 9 rises to contact the switch. For example, this switching function can be used to shut off a pump that directs liquid 8 into the tank. Switch 7, on the other hand, is a low-level switch and is typically covered with liquid or "wet." Switch 7 performs a switching function or outputs an alarm when the liquid surface 9 drops below the switch's level. The latter switching function can activate a pump to direct more liquid into the tank.

[0034] The changes and trends in the resonant frequency of a vibrating tuning fork level switch when completely dry or completely wet can be used to monitor the operating condition of the tuning fork. In particular, changes in the tuning fork's characteristics caused by corrosion or coating of the tines will be reflected in the change in the resonant frequency of the tuning fork when dry and wet. When operating normally and correctly, the resonant frequency of the vibrating tuning fork level switch will fluctuate slightly when completely dry or completely wet, but will remain as Figure 2 、 Figure 3 and Figure 4 The terms "completely dry" and "completely wet" mean that the tuning fork tines are not immersed at all or are completely immersed in the process liquid, respectively.

[0035] Figure 2 、 Figure 3 and Figure 4 The bandwidth in is set empirically and lies between [f 干燥 -2σf 干燥 +2σ] or [f 湿润 -2σf 湿润 +2σ], the frequency bands in these graphs include known sensitivities to changes in process conditions (e.g., temperature, pressure, and liquid density).

[0036] The frequency of a vibrating tuning fork level switch in a completely dry state is a reliable indicator of the fork's health, taking into account factors such as corrosion or coating of the fork tines. By presetting an acceptable threshold range for the tuning fork's resonant frequency in a completely dry state, the resonant frequency of the device in its original position and in a known completely dry state can be compared, enabling the health of the vibrating tuning fork level switch to be determined. If this check is performed periodically and the obtained resonant frequencies are stored in the device's memory, simple trend analysis of the historical resonant frequency data can be obtained, which can provide a clear indication of the device's service life.

[0037] The resonant frequency of the tuning fork in the fully wetted state will depend on the properties of the process liquid, so a threshold range for normal wetting frequencies must be set during the device's initial installation or during factory calibration using a sample of the process liquid used with the device. By presetting an acceptable threshold range for the tuning fork's resonant frequency in the fully wetted state, the resonant frequency of the device in situ and in a known fully wetted state can be compared, thereby determining the health of the vibrating tuning fork level switch. If this check is performed periodically and the obtained resonant frequencies are stored in the device's memory, simple trend analysis of the resonant frequency history can be obtained, providing a clear indication of the device's service life.

[0038] Whether the comparison is made when the switch is completely dry or completely wet, confirmation of the wet / dry status is essential because the indication from the switch itself cannot be relied upon. This is because factors that arise during service can lead to false indications. For example, the switch may have been damaged during installation, causing it to resonate at a frequency outside the preset frequency band. Additionally, material from the process liquid may bridge the space between the tines of the tuning fork, resulting in a false wetness indication when, in fact, the tines are above the liquid level. Embodiments of the present invention address this issue by providing a method for verifying whether the tuning fork tines are wet or dry, independent of the switch; while the switch remains in place on the tank.

[0039] Return to reference Figure 1 As described above, switch 6 is used as a high level alarm, and switch 7 is used as a low level alarm. In addition, another independent level measurement device 10 (e.g., a continuous ultrasonic / radar level transmitter) can be adopted and configured to define the completely wet condition and the completely dry condition as follows:

[0040] *Completely dry condition: Liquid level 9 < D2 for level switch 6

[0041] *Fully wetted condition: Liquid level 9> D1 for level switch 7

[0042] D1 and D2 are set empirically, but taking into account possible measurement errors caused by the liquid level transmitter 10. For example only, D1 may be 20 cm higher than the installation position of the vibrating tuning fork liquid level switch 7, and D2 may be 20 cm lower than the installation position of the vibrating tuning fork liquid level switch 6.

[0043] With the device 10 in position on the tank 5, two suggested ways of carrying out the authentication process according to the invention will now be described.

[0044] In a substantially manual process, the field service engineer obtains the wet or dry status of the switches 6 and / or 7 using the apparatus 10 or by visual inspection. The field service engineer may then provide an indication of the status of the switch (or one of the switches) to the host system 3 and / or invoke a health check function of the switches 6 and 7 via a local operator interface (LOI) included in the switch or, for example, via a communication protocol such as HART or a fieldbus. In providing the indication of the status to the host system 3 of the monitoring system 1, the host system 3 may obtain a reference value and a current value of an operating parameter from the level sensing device 6 and / or 7, compare the reference value with the current value, and provide an output indicating the status of the level sensing device based on the comparison and the indication provided by the field service engineer. For example, the output may be provided in a manner such as Figure 1 In the case of providing an indication of status to a liquid level sensing device (liquid level switch), a processor within the liquid level switch is configured to then compare the switch's currently observed resonant frequency with an appropriate wet or dry preset threshold range and provide an output indicative of the operating condition. For example, the output may be a signal indicating "OK operating condition," "Caution," or "Alarm," depending on whether the current frequency is within the preset threshold range, on the limit of the preset threshold range, or outside the preset threshold range. The observed resonant frequency is then stored in a memory of the switch along with a timestamp. The continuously stored frequencies may be processed to provide an indication of switch condition trends.

[0045] In a more automated embodiment, the present invention actively combines the level switches 6 and 7 with another, for example, continuous radar / ultrasonic level transmitter 10, to provide a full level control and monitoring system 1 for industrial process tanks, in which the level switches 6 and 7 provide high and low alarm level indicators, and the transmitter 10 provides an indication of the current level. Both the level transmitter 10 and the level switches 6 and 7 can be configured with a communication protocol such as HART or a fieldbus. Using the HART communication protocol as an example, during installation, the devices 6, 7, and 10 can be arranged in a communication loop, wherein the level transmitter 10 is configured as a secondary master device that broadcasts the measured tank level to all HART-equipped devices in the loop at regular intervals (e.g., daily, weekly, or monthly). The resulting tank level information is preferably encrypted for security. As receivers, the vibrating fork level switches 6 and 7 will monitor the broadcasted tank levels and can therefore verify whether they are completely dry or completely wet. Once the tuning fork state is established, the above comparison can be made, an output provided, and the frequencies observed at regular time intervals stored and processed to provide trend information.

[0046] According to another example configuration of monitoring system 1, host system 3 can acquire signals from level transmitter 10 and from level sensing devices 6 and 7, and automatically determine the status of level sensing devices 6 and 7 based on the acquired signals. Specifically, host system 3 can acquire a signal from level transmitter 10 indicating the current level of liquid in tank 5, and determine, based on the signal acquired from the level detection device and the known level of liquid in the level sensing device, whether the level sensing device is wet or dry when the current value of the operating parameter is acquired by the processor of the level sensing device. Based on this determination and a comparison between the reference value of the operating parameter and the current value of the operating parameter, host system 3 can estimate the current condition of level sensing devices 6 and 7. At least one reference value for the operating parameter of level sensing devices 6 and 7 can be maintained in a database in host system 3, associating the identity of a particular level sensing device with the at least one reference value for its operating parameter. Alternatively, each level sensing device can maintain its at least one reference value for its operating parameter in its own memory, which can facilitate the installation of new level sensing devices in monitoring system 1.

Claims

1. A method of monitoring a condition of an apparatus, the apparatus being configured to determine a level of a liquid in a container, the apparatus comprising an actuator, the actuator being configured to exhibit different values ​​of an operating parameter depending on whether the actuator is wet or dry, the method comprising the steps of: providing at least one reference value of an operating parameter, the at least one reference value indicating whether the device is completely above the liquid ("dry") or completely immersed in the liquid ("wet"); obtaining, by the device, a current value of the operating parameter; determining, independently of the device, whether the device was wet or dry when obtaining the current value of the operating parameter; comparing a current value of an operating parameter acquired by the device with at least one reference value of the operating parameter; as well as Based on the comparison and the determination of whether the device is wet or dry, an output is provided indicative of a condition of the device.

2. The method according to claim 1, wherein At least one reference value of the operating parameter is stored within the device.

3. The method according to claim 1, wherein The device is a vibrating tuning fork liquid level switch configured to operate in resonance; At least one reference value of the operating parameter includes a resonant frequency range of the vibrating tuning fork liquid level switch when dry and when wet, respectively; and The current value of the operating parameter is the current value of the resonant frequency.

4. The method according to claim 1 or 2, wherein: The step of determining whether the device is wet or dry is performed by manual observation.

5. The method according to claim 1 or 2, wherein: The step of determining whether the device is wet or dry is performed using a separate liquid level detection device.

6. The method according to claim 1 or 2, wherein: The step of providing an output indicative of a condition of the device includes transmitting an output indicative of a condition selected from the group consisting of "OK," "Caution," and "Alarm." 7. The method according to claim 1 or 2, further comprising the steps of: storing current values ​​of the operating parameters obtained at different times to obtain stored time series values; as well as One or more trends indicative of physical changes to the device are determined based on the stored time-series values.

8. A liquid level sensing device for determining the liquid level of a liquid in a container, the liquid level sensing device comprising: a memory for storing at least one reference value of an operating parameter, the at least one reference value indicating whether the device is completely above the liquid ("dry") or completely immersed in the liquid ("wet"); an actuator configured to exhibit different values ​​of an operating parameter depending on whether the actuator is wet or dry; as well as a processor coupled to the actuator and configured to: obtaining a current value of an operating parameter from the actuator; receiving a result of determining, performed independently of the device, whether the device was wet or dry when the current value of the operating parameter was obtained; comparing a current value of an operating parameter acquired by a processor coupled to the actuator with at least one reference value of the operating parameter stored in the memory; as well as Based on the comparison and the determination of whether the device is wet or dry, an output is provided indicative of a condition of the device.

9. The liquid level sensing device according to claim 8, wherein: The actuator is a vibrating tuning fork.

10. A liquid level sensing system comprising: The liquid level sensing device according to claim 8 or 9; as well as A liquid level detection device is arranged and configured to determine the level of liquid in a tank.

11. The liquid level sensing system according to claim 10, wherein: The liquid level detection device is an ultrasonic transmitter or a radar liquid level transmitter.

12. The liquid level sensing system according to claim 10, wherein: The liquid level sensing device and the liquid level detection apparatus are configured to communicate via a common communication protocol.

13. A monitoring system for monitoring the status of a container, comprising: a level sensing device for determining a level of liquid in the container, the level sensing device comprising an actuator configured to exhibit different values ​​of an operating parameter depending on whether the actuator is wet or dry; and a processor coupled to the actuator and configured to obtain a current value of an operating parameter from the actuator; as well as a host system in communication with the liquid level sensing device, the host system including processing circuitry configured to: receiving a current value of an operating parameter from the fluid level sensing device; comparing a current value of an operating parameter to a reference value of the operating parameter indicating whether the level sensing device is completely above the liquid ("dry") or completely immersed in the liquid ("wet"); as well as An output indicative of a condition of the device is provided based on the comparison and based on a determination, performed independently of the level sensing device, whether the level sensing device is wet or dry when a current value of an operating parameter is acquired by a processor of the level sensing device.

14. The monitoring system according to claim 13, wherein: The reference value of the operating parameter is stored in a memory included in the liquid level sensing device; and The processing circuit of the monitoring system is further configured to obtain a reference value of the operating parameter from the liquid level sensing device.

15. The monitoring system according to claim 13, wherein: The monitoring system further comprises a level detection device arranged and configured to determine the level of the liquid in the tank; and The processing circuitry of the monitoring system is further configured to: obtaining a signal from the liquid level detection device indicating the current liquid level in the tank; and Based on the signal obtained from the level detection device and the known level of the fluid in the fluid level sensing device, it is determined whether the fluid level sensing device is wet or dry when a current value of an operating parameter is obtained by a processor of the fluid level sensing device.

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