阅读说明：本技术 振动音叉液位开关的改进或与其有关的改进 (Improvements in or relating to vibrating tuning fork level switches ) 是由 张敬东 塔德沃斯·策加泽亚布 安德鲁·大卫·麦克赖尔 于 2020-02-07 设计创作，主要内容包括：本发明提供了用于检查自振荡振动音叉液位开关的状态的方法以及设备。该开关包括测试设备,该测试设备在开关从闭合回路反馈操作模式进入断开回路测试模式时进行操作。接收到的测试信号的幅度与预定阈值进行比较,以确定开关的健康状况。(The invention provides a method and a device for checking the state of a self-oscillating vibrating tuning fork level switch. The switch includes a test device that operates when the switch enters an open loop test mode from a closed loop feedback mode of operation. The amplitude of the received test signal is compared to a predetermined threshold to determine the health of the switch.)

1. A method of testing the function of a vibrating tuning fork level switch configured to self-oscillate in a normal operating mode by means of a closed feedback loop, the method comprising: interrupting the normal operating mode; driving the switch in an open loop pulsed mode of operation with a test signal generated by a test device integrated into the switch; and comparing the amplitude of the test signal received at a set of times to a predetermined amplitude threshold at the corresponding time.

2. The method of claim 1, wherein the received test signal is subjected to envelope detection.

3. A method according to claim 1 or 2, wherein the test signal is generated at a frequency related to a frequency observed in normal mode operation prior to interrupting the normal mode of operation.

4. The method of any of claims 1-3, wherein the switch comprises an integral microcontroller, the method comprising: generating the test signal using the microcontroller.

5. The method of claim 4, comprising: a discrete number of cycles of the test drive signal is generated.

6. The method of claim 4 or 5, further comprising: programming the microcontroller to interrupt the normal operating mode prior to generating the test signal.

7. The method of any of claims 1-5, wherein the act of interrupting the normal operating mode is accomplished by manual intervention.

8. The method of claim 7, wherein the manual intervention is effected from a remote location.

9. The method of any preceding claim, further comprising: providing a visual indication of the state of the switch.

10. The method of claim 9, comprising: an indication of the presence of the fault and the nature of the fault is provided.

11. A vibrating tuning fork level switch configured to self-oscillate in a normal operating mode by means of a closed feedback loop, the switch further comprising a test device operable in an open loop pulse test mode when the normal operating mode is interrupted, the test device being configured and operable to: the switch is driven with a test signal and the amplitude of the test signal received at a set of times is compared to a predetermined amplitude threshold at the corresponding time.

12. The vibrating tuning fork level switch of claim 11, further comprising: an envelope detection device configured to be applied to a received test signal.

13. The vibrating tuning fork level switch of claim 11 or 12, wherein the test equipment is configured to: the test signal is generated at a frequency related to a frequency observed in normal mode operation prior to interrupting the normal mode of operation.

14. A vibrating tuning fork level switch according to any one of claims 11 to 13, comprising an integral microcontroller in which the test device is at least partially integrated.

15. The vibrating tuning fork level switch of claim 14, wherein the microcontroller is configured or programmed to generate a discrete number of cycles of the test signal.

16. A vibrating tuning fork level switch according to claim 14 or 15, wherein the microcontroller is programmed to interrupt the normal operating mode prior to operation of the test device.

17. A vibrating tuning fork level switch according to any one of claims 11 to 15, further comprising a controller for effecting interruption of the normal operating mode and initiating operation of the test equipment.

18. The vibrating tuning fork level switch of claim 17, wherein the controller is manually or remotely operable by a manual control intervention or a process control intervention.

19. A vibrating tuning fork level switch according to any one of claims 11 to 18, wherein the test apparatus is further operable to provide a visual indication of the state of the switch.

20. The vibrating tuning fork level switch of claim 18, comprising an LED light programmed to indicate the presence of a fault and the nature of the fault.

Technical Field

The present invention relates to vibrating tuning fork level switches, and in particular, to a method of checking the state of a vibrating tuning fork level switch in situ; and to a vibrating liquid level tuning fork configured to implement such a method.

Background

Vibrating tuning fork level switches are commonly used to detect when the surface of the liquid in the tank is at a particular level, which is the height at which the tuning fork is located in the tank. Typically, tuning fork level switches are configured to self-oscillate through a positive feedback loop in the electronic circuit, wherein the phase delay between the transmit and receive elements is carefully tuned to ensure that the positive feedback signals are in phase.

In operation, in a "normally dry" application, the vibration frequency will be at a level when the tuning fork is in air ("dry"), but will drop when the liquid in the tank rises to contact the tuning fork ("wet"). In "normal wet" applications, the opposite applies, and the frequency will increase as the liquid falls below the liquid level of the tuning fork.

Although relatively simple in construction, vibrating fork level switches are used in situations where economic and personal losses can occur if the switch fails to operate as intended. Therefore, especially in safety critical applications, the switch function needs to be checked from time to time.

Past inspection switches typically involved: closing the process of using the switch; removing the switch; a test switch; reinstalling the switch; and restarting the process. The test procedure involves contacting the tuning fork with a liquid or other damping element to simulate the wet or dry condition of the switch. Such procedures necessarily involve the service operator being on site, but may also involve the breaking of seals and exposing the service operator to unpleasant and/or hazardous materials.

EP 1580539 proposes a method for testing a vibrating tuning fork having a feedback circuit configured to oscillate the tuning fork at its resonant frequency. The described method proposes to vary one or more excitation parameters within the circuit that remains self-oscillating and then compare the resulting variation with a data set comprising data of a corresponding fault-free system. The excitation parameters are reflected in the signal processing block under control of the microprocessor. The microprocessor, according to the description, alters the operation of one of these processing blocks to create a test, but it is not understood how such an approach would actually be implemented, since the feedback circuit is carefully balanced and the parameters of the perturbation circuit would prevent its operation.

EP 1624291 proposes an alternative in which the tuning fork is driven at a frequency exceeding the resonant frequency range and the resulting amplitude signal is then analysed. This device requires additional driving circuitry and is not able to diagnose faults in the function of existing circuits.

US 2006/0267784 describes a tuning fork level switch which implements the test function in the operating microprocessor. When the tuning fork is "dry", the functional test unit reduces the amplification of the input amplifier during functional testing to generate a test measurement signal that would be generated if the tuning fork was wet. The evaluation unit then evaluates the test measurement signal as a "wet" signal without error.

It is an object of the present invention to provide a method and/or device for checking the functionality of a switch, which will solve at least to some extent the above-mentioned problems and disadvantages of the prior art; or the method and/or apparatus will at least provide a novel and useful choice.

Disclosure of Invention

Accordingly, in one aspect, the present invention provides a method of testing the function of a vibrating tuning fork level switch configured to self-oscillate in a normal operating mode by means of a closed feedback loop, said method comprising: interrupting the normal operating mode; driving the switch in an open loop pulse mode with a test signal generated by a test device integrated into the switch; and comparing the amplitude of the test signal received at a set of times to a predetermined amplitude threshold at the corresponding time.

Preferably, the received test signal is subjected to envelope detection.

Preferably, the test signal is generated at a frequency related to a frequency observed in normal mode operation prior to discontinuing the normal mode of operation.

Preferably, the switch comprises an integral microcontroller, the method comprising: generating the test signal using the microcontroller.

Preferably, the method comprises: a discrete number of cycles of the test drive signal is generated.

Preferably, the method further comprises: programming the microcontroller to interrupt the normal operating mode prior to generating the test signal.

Alternatively, the act of interrupting said normal operating mode is effected by manual intervention.

Preferably, said manual intervention is effected from a remote location.

Preferably, the method further comprises: providing a visual indication of the state of the switch.

Preferably, the method comprises: an indication of the presence of the fault and the nature of the fault is provided.

In a second aspect, the present invention provides a vibrating tuning fork level switch configured to self-oscillate in a normal operating mode by means of a closed feedback loop, the switch further comprising a test device operable in an open loop pulse mode when the normal operating mode is interrupted, the test device being configured and operable to: the switch is driven with a test signal and the amplitude of the test signal received at a set of times is compared to a predetermined amplitude threshold at the corresponding time.

Preferably, the vibrating tuning fork level switch further comprises an envelope detection device configured to be applied to the received test signal.

Preferably, the test device is configured to: the test signal is generated at a frequency related to a frequency observed in normal mode operation prior to discontinuing the normal mode of operation.

Preferably, the vibrating tuning fork level switch comprises an integral microcontroller, the testing device being at least partially integrated in the microcontroller.

Preferably, the microcontroller is configured or programmed to generate a discrete number of cycles of the test signal.

Preferably, the microcontroller is programmed to interrupt the normal operating mode prior to operation of the test device.

Alternatively, the vibrating tuning fork level switch further comprises a controller for effecting interruption of the normal operating mode and initiating operation of the test device.

Preferably, the controller is manually or remotely operable by manual control intervention or by process control intervention.

Preferably, the test device is further operable to provide a visual indication of the state of the switch.

Preferably, the vibrating tuning fork level switch comprises an LED light programmed to indicate the presence of a fault and the nature of the fault.

Those skilled in the art will appreciate that many variations of the manner in which the invention may be practiced. The following description is intended only as an illustration of one means of carrying out the invention and the absence of a description of variants or equivalents should not be taken as limiting. Within the scope of the appended claims, the description of a particular element should be considered to include any and all equivalents thereof as may exist in the present or future, where possible.

Drawings

A preferred form of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1: a schematic hardware diagram for performing fault detection according to the present invention is shown;

FIG. 2: showing the frequency response of a vibrating tuning fork level switch operating in air, wherein the frequency of the drive signal is at the tuning fork's resonant frequency in air;

FIG. 3: showing the frequency response of a vibrating tuning fork level switch operating in water, wherein the frequency of the drive signal is at the resonant frequency of the tuning fork in water;

FIG. 4: showing the frequency response of a vibrating tuning fork level switch operating in silicone oil at the resonant frequency of the tuning fork; and

FIG. 5: showing the frequency response of a vibrating tuning fork level switch operating as in figure 4 but not at resonance and indicating the presence of a fault, the amplitude scale is less than that of figure 4.

Detailed Description

Referring to the drawings, the present invention provides a method of checking the operation and/or status of a vibrating tuning fork level switch 10 without removing or disturbing the switch from its normal operating position. The present invention also provides a level switch configured with internal fault checking or testing equipment so that the function of the switch can be checked or tested when the switch is in place. As will be clear from the description below, the test procedures and equipment may also include fault finding and diagnosis.

Referring to fig. 1, conventionally, a level switch 10 operates in a self-oscillating mode, a tuning fork 12 is driven by a piezoelectric driving element Tx 13, and the resulting tuning fork vibration is sensed by a piezoelectric sensing element Rx 14. In a conventional manner, a positive feedback loop in an electronic circuit containing suitable amplifiers and filters establishes and maintains the tuning fork 12 vibrating in a resonant manner. The Rx signal is also fed to a waveform shaper 15 and thence to a microcontroller 16 which compares the Rx frequency to one or more thresholds to determine if there has been a change in the medium in contact with the tuning fork 12.

In its broadest form, the present invention relates to the integration of test equipment into the switch 10. This is conveniently achieved by adding additional hardware, such as additional drivers and receive amplifiers, to the microcontroller 16 which enable the normal operating cycle of the switch to be interrupted and the open loop test mode to be initiated in which a test signal is generated to drive the existing transmit element 13 to vibrate the tuning fork. The response to the test signal is then picked up by the existing Rx sensor 14 and preferably subjected to analysis by passing the received test signal to an envelope detector 17 where the amplitude of the received test signal is recorded and compared by the microcontroller 16 to a predetermined threshold for a given set of times. Essentially, this enables the rate of decay of the test signal to be observed. Based on the comparison with the known data, the pattern of received signal attenuation can be translated into an indication of the health of the vibrating tuning fork sensor. The indication may then be output by a visual indicator, such as an LED light 18.

In order to enable the normal self-oscillating mode of operation of the switch 10 to be interrupted and to drive the tuning fork 12 in the open loop test mode, it is convenient to include a gate switch 20 in the feedback loop so that the feedback can be interrupted and a test signal from the microcontroller 16 applied to the transmitting element 13. At the end of the test period, the door switch is repositioned to reestablish the operational closed feedback loop. The door switch may be operated under the control of the microcontroller 16, or may include additional controls that allow external intervention to effect the switching. The additional control may allow manual operation of the door switch 20 and/or may allow remote operation of the door switch via wired or wireless communication devices.

Conveniently, the test signal is a 50 cycle square wave, and the frequency of the test signal can be set in a number of different ways.

First, the test frequency may be set to a normal "dry" or a normal "wet" frequency depending on what the switch indicates immediately before the test cycle begins. Secondly, the frequency observed before the interruption of the operating mode and the start of the test period is used for the test signal. A third option is to apply a test period over a range of frequencies, looking for the point at which the tuning fork will resonate. It is clear that if no resonance is observed during the sweep of this different frequency, it can be concluded that the switch is not functioning.

Those skilled in the art will appreciate that the microcontroller 16 may be programmed to implement any one or more of the options described above.

After sending the test signal, the resulting response or received signal is passed to an envelope detector 17. Thereafter, the microcontroller 16 samples the amplitude within the envelope by means of the analog-to-digital converter 21 in time, for example 0.2ms, 20ms, 40ms, 60ms and 80 ms. The amplitude at each point in time is then compared to a preset threshold to determine whether the switch is operating in an acceptable manner. As described above, a visual indication of the health of the switch may be provided by the LED light 18. The LED lamp 18 may in turn be programmed to indicate a different form of fault.

Referring now to fig. 2, the test transmit pulse is shown at the bottom of the figure, while the response of the tuning fork in air is shown at the top of the figure. It is noted that the signal decay at the termination of the test pulse is relatively gradual, indicating that the switch is in good condition.

Figure 3 shows a similar test to figure 2 but with the tuning fork in water. Although the amplitude of the received signal or response is overall low, due to the damping effect of the water, the decay after termination of the transmitted test pulse is again relatively gradual, indicating that the switch is in good condition.

Fig. 4 and 5 are simulations providing a comparison between a switch in a good operating condition and a faulty switch. Figure 4 shows the response of a switch operating in a fairly viscous (1086cp) silicone oil. Even though the switch may be in good condition, the response decays rather quickly upon termination of the test signal, as expected in fluids of such viscosities. Fig. 5 is a simulation of a defective switch operating under the same conditions. In fig. 5, the amplitude (vertical) ratio is nearly twice that of fig. 4, so even when the test signal is still transmitting, the amplitude of the received signal is depicted as being about half that of fig. 4. Assuming that the transmitted or test signals are the same, this is an indication that there is a fault in the switch.

As mentioned above, the invention enables identification and indication of faults, such as:

when dry, correct/incorrect tuning fork state

Correct/wrong tuning fork state when wet

Disconnection in switch

Disengagement or engagement decay in the sensor drive/receive assembly;

the tuning fork tip is damaged.

These faults can be characterized by appropriate programming of the microcontroller 16 and individually indicated by programming the operation of the LED lights 18, for example by assigning different flashing rates or different colors to different faults.

Thus, the present invention not only enables testing of a vibrating tuning fork level switch in situ, but also can remotely test a vibrating tuning fork level switch by using communication devices in such switches, which has considerable advantages in the art.