Patent Application
20210172432
The monitoring and surveillance of air operated diaphragm pumps to determine the number of pulses which has been conducted with a given pump is challenging, however important as an air operated diaphragm pump shall only survive a predefined number of pulses in a given environment due to diaphragm wear during pumping action. In order to avoid brake down during operation it is thus required, that a precise measure of pump strokes is obtained, such that the membrane may be changed in a planned maintenance operation, which does not adversely affect the operation of a plant comprising the pump.
It is known to add stroke counters fitted to the air exhaust system; however, such elements are prone to be un-reliable and are not necessarily capable of detecting erratic pump action due to different kinds of mal function.
Thus, there is a need for a method and an apparatus which enables reliable and fail-safe detection of pump strokes and which eliminates the above-mentioned disadvantages of the prior art.
A method for surveillance of an air operated diaphragm pump is provided whereby initially an accelerometer with at least 3 orthogonal accelerometer measuring directions is attached to an air operated diaphragm pump or to a structure directly connected with an air operated diaphragm pump; agitation level of the accelerometer at a frequency rate above a predefined pulse rate of the air operated diaphragm pump is registered, and a base line noise level of the accelerometer agitation level during a period of no pump action is measured and stored, and a pulse rate of the air operated diaphragm pump is determined as the most significant frequency of pulses out of an entire power spectrum calculated from the accelerometer readings, and lastly the most significant frequency of pulses and the duration of registered pulse signals is determined and stored.
Based on the pulse frequency which is determined as the most significant frequency in the power spectrum and the duration of pulse or stroke action of the air operated pump, it is now easy to determine the number of stroke actions provided within a given time frame, and to also store this value.
By this method, a total number of stroke actions of a given pump may continually be surveilled, and the surveillance date may be used for the generation of alerts, in case the pump action is not according to plan, or an end of life for the membrane is approaching. Maintenance, such as the exchange of a pump membrane may be initiated timely and in a controlled manner, which does not negatively affect the operation of the plant in which the pump servs.
In an aspect of the invention the frequency spectrum for the accelerometer readings is determined from calculated values: aRMS(i) based on sampled accelerometer readings at a sampling rate whereby,
and where i is the sample number, and M is the number of samples used to calculate the value aRMSi, at sample number i, and further
a=a
Total(i)=√{square root over (X2(i)+Y2(i)+Z2(i))}
where Xi, Yi and Zi are normalized accelerometer output values in orthogonal directions x, y and z respectively in each sample. It is the atotal(i) values which are used in the calculation of the aRMS(i) values. Normalization if the Xi, Yi and Zi values are performed in a usual manner in order to exclude bias from gravitation so that only accelerations due to the movements of the pump are included in the calculations.
The aRMS(i) time dependent values are indicative of the energy levels contained in the accelerometer signal and thus indicative of the agitation level of the pump at a particular sample. The M value, which counts the number of samples going into calculating each aRMS(i) value determines, together with the sampling rate for the accelerometer signal, the frequency resolution of the calculated power spectrum.
In an aspect of the invention, M is chosen such that at a given sampling rate, the duration of the M samples spans a time of no more than half the time of a pulse duration during normal operation of the pump being monitored. In this way it is ensured, that the pump stroke signal is sure to show up in the power spectrum as a frequency with a significant energy content.
In an aspect of the invention an externally threaded part of an accelerometer housing is rotated into a threaded connection pipe or threaded pipe bracket located on a suction or pressure pipe leading to/from the air operated diaphragm pump whereby the distance between the connection pipe or bracket and the pump is adapted to be no more than 6 times the pipe diameter of suction or pressure pipe respectively, or preferably no more than 4 times the pipe diameter og most preferred no more than 2 times the pipe diameter. The working medium which the pump is to pressurize, shall also flow to/from the pump in accordance with the stroke rate of the pump, and thus the pipes leading to and from the pump and feeding the medium to the volume changing cavities in front of the membranes, shall vibrate in accordance with the stroke rate, at least close to the pump itself. Thus, it is preferred that the housing and accelerometer is provided close to the pump.
In this way it is assured, that the accelerometer shall be intimately connected to the vibrating part of the pump to be followed. Also, these pumps are usually connected with pipes, such as water pipes, and here, it is easy to connect the threaded stub to a connection pipe, such as an open pipe-end having internal threads. The threaded connection ensures a play-free connection between the accelerometer housing and the pump or pipe connection. Such a play free connection is important in ensuring that resonance frequencies of pipes and accelerometer housing are not energized by the sometimes-fierce vibrations of these pumps. It further allows the accelerometer housing to be added to the pump or pipes at the pump without use of specialized tools, and in fact the mounting of the accelerometer housing may be done by hand. The threads on the exterior of the stub shall be chosen according to the threading standard, which is most prominent in the country or region, where the pump is installed. The use of a simple treaded stub is also instrumental in ensuring, that the pump rate may be calculated fail safe with the relatively simple calculations given above.
In an aspect of the invention the following steps are performed:
The determined pulse rates which have been collected at regular intervals allows for the pump to be monitored or surveilled, such that any un-foreseen events may be observed centrally for any number of pumps equipped with the surveillance means.
In an aspect of the invention an accelerometer housing houses a sub-giga radio which receives pulse rate data from one or more accelerometers at nearby pumps and feeds these pulse rate data through a cellular device via a cellular connection to a data repository located away from the cellular device. The data are wirelessly transmitted to a remote data repository and this will potentially create a digital version of a life story of the pump, which if compared to life stories of other pumps may provide valuable data concerning the reliability of a single pump, classes of pumps or populations of pumps working with similar media.
In a further aspect of the invention NFC signals are captured within the housing when an NFC enabled device such as a cell phone is placed in the vicinity of the housing. Such NFC signals are used to modify a content of a control device which control device facilitates the accelerometer measurements. In this way, an operator may change settings locally based on observed events and conditions around the pump in question.
In a further aspect the control device is adapted to monitor a pulse rate from a pump, and to provide an alert in case pulse rates are not within predetermined limits. This allows a close monitoring of a pump locally, such that immediate alerts may be provided to anyone in the vicinity of the pump.
The invention further relates to a surveillance device comprising a:
In order to ensure, that accelerometer readings are sufficiently representative of motions of a given air operated diaphragm pump, the accelerometer housing shall have to be play-free and forcefully connected to the pump or piping connected to the pump. This is ensured by the externally treaded stub of the accelerometer housing and its being threadedly connected to an internally treaded connection pipe or bracket at or connected with an air operated diaphragm pump.
In an aspect of the invention the surveillance device is adapted to calculate an overall energy level measure based on registered accelerometer values in 3 orthogonal directions whereby a frequency spectrum for the overall energy level measure is determined from calculated values:
and where i is the sample number, and M is the number of samples used to calculate the value aRMS, at sample number i and further
a=a
Total(i)=√{square root over (X2(i)+Y2(i)+Z2(i))}
where Xi, Yi and Zi are normalized accelerometer output values in orthogonal directions x, y and z respectively in each sample.
Hereby a secure and precise detection of the frequency spectrum for the energy level at the accelerometer is provided, such that pump stroke rate may be securely and precisely calculated when the frequency spectrum of the energy levels has been determined. A frequency spectrum based on the data here will display a dominant frequency line at the pulsation rate or pulsation frequency of the pump. And as these pulsations of the pumps are always periodic, they do not change significantly over time and further, the noise energy level is far below the energy level of the signal generated by the pulsations of the pump at the pulsation frequency.
In an aspect of the invention, the externally threaded part of the accelerometer housing is rotated into a threaded connection pipe or threaded pipe bracket located on a suction or pressure pipe to/from the air operated diaphragm pump whereby the distance between the connection pipe or bracket and the pump is adapted to be no more than 6 times the pipe diameter of suction or pressure pipe respectively, or preferably no more than 4 times the pipe diameter og most preferred no more than 2 times the pipe diameter.
Hereby it is ensured, that the obtained measurement data may be used in the calculation of the pump rate without the possibility of resonance frequencies of other parts of the system being energized to levels, where they might disturb the measurements.
In an aspect of the invention the device further comprises a PCB (printed circuit board) which PCB is mounted with the control device, a radio transmitter adapted to transmit captured accelerometer data and the accelerometer. The accelerometer may be a micromechanical device such as a MEMS device and thus adapted to be mounted onto a PCB. PCB parts may be screwed onto and thus secured unmovably to any inside part of the accelerometer housing.
In a further aspect of the invention an NFC enabled communication device and a sub-giga radio are provided at the PCB. This allows communication to and from the housing in various wireless formats, such as through the short-range NFC channel, which is part of many telephones and similar devices, and through a sub-giga radio transmission, which is used for standardized communication and data exchange in many industries.
In a further aspect of the invention, a battery is housed in the housing and connected to the PCB in order to energize the electric parts mounted thereon. This allows the device a stand-alone capability which is most important in places where electric power cables are not easily provided.
In yet a further aspect of the invention, the control device is adapted to provide an alarm in case the calculated pump rate is not according to expectation. In this way, the surveillance device also shall work as a stand-alone device, and still provide important benefits even if not in connection with a remote data repository.
In a further aspect, the surveillance device has a visual display which is mounted on the housing.
The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:
Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a housing 1 of the present invention is illustrated in
The cradle comprises a PCB element 8, which is mounted therein, and is equipped with a range of components.
In
When the stub 6 is connected to an internally threaded connection pipe at or near an air operated membrane pump, the vibrations generated by the pump shall be transmitted to the stub through the pipes, whether they be feed pipes to the pump or delivery pipes from the pump.
In
The lid 3 has internally arranged threads on the skirt thereof, and these are adapted to engage externally arranged corresponding threads on the cradle 2 on a raised portion thereof.
The elastomeric safety band 4 is adapted to be preyed onto the assembly of cradle 2 and lid 3 to assume the position disclosed in
In
In
The digital input port 18 may be connected through a digital input line 22 to external devices such as a high-speed counter in order to register strokes or flowmeter data.
The two analog input connectors 7 may be connected to external sensors, and also these input channels may be programmed to receive current or voltage signals according to need.
Further, a pressure/leek sensor 21 may be provided in the housing along with current/voltage sensors 20.
With reference to
The algorithm provided in the block diagram may be implemented by an analog circuits or digital logic or by software or any combinations of these (Processor, FPGA, ASIC etc.).
It is generally assumed that:
In a digital embodiment of the invention with a medium size air operated diaphragm pump, the following parameters are chosen:
The accelerometer measures the acceleration x, y and z in all 3 axes. The accelerometer measurements include acceleration related to the strokes and surrounding vibrations as well as the constant acceleration of gravity. The gravity acceleration does not contribute to the pulses vibrations and is eliminated in the usual manner as mentioned.
Calculating the constant component from gravity is provided by:
The zero offset acceleration becomes:
X=x−μ
x,
Y=y−μ
y,
Z=z−μ
z
The total magnitude of acceleration of each sample i, is
a
Total(i)=√{square root over (X2(i)+Y2(i)+Z2(i))}
The measured acceleration is composed from the power of the vibrations induced by the pump, the power of other sources of vibrations in the vicinity and from additive noise. It is desired to reduce the effect of the additive noise. For this purpose, a Low Pass Filter (LPF) is applied.
An RMS filter is selected for its additional property of emphasizing temporal elevation in the power. The temporal power of the total acceleration magnitude is estimated by local RMS calculation. The RMS is calculated by a moving filter of length M:
M is selected to be 5 which reflects a cut-off frequency of ˜10 Hz and an estimation of the power over a period of
in time.
The periodic pulses are detected based on the spectral topology (frequency domain) of the calculated RMS signal. Periodic pulses in the time domain are transformed into evenly spaced pulses or spectral lines in the frequency domain as well. Whereas the lowest frequency pulse is the based pulse, having the frequency corresponding to pump stroke rate.
Since the aRMS data still contains some random noise, the frequency domain is estimated by Power Spectral Density (PSD).
In the frequency domain, only periodic pulses are transformed into distinguished spectral peaks. Finding the frequency in which the first spectral peak is detected obtains the frequency of the pulses.
Since a cycle of the pump contains two pulses (both sides) the actual rate of the pump is slower by factor of 2 from the measured pulse rate.
Based on assumption (1), pulses having power weaker than the pump stroke power are not related to a pump stroke action. The level of power that indicates the power of a pump stroke depends on the pump interface to the surrounding frame and on the environment.
This must be calibrated on each individual pump. In the case of zero pulse rate (pump is off), the accelerometer sensors may still detect pulse rates due to periodic noise pulses, stemming from sources such as other pumps drawing air from the same air supply line, or feeding liquid into the same pump line or transmitting vibrations to the accelerometer through fixed construction parts. The classification of such noise as noise is based on the power level of the detected real pump pulse. The value of a parameter PULSE_THRESHOLD must be calibrated for each further pump to ensure fail-safe detection of a no-stroke situation.
Accelerometers are sensitive to any force applied to the subject. Thus, the measurements are noisy. The algorithm avoids the detection of noise as pump induced pulses. Random noise in general has low power compared to the power of pump stroke pulses and therefore random noise is not detected. A single erratic high-power pulse might be detected but since it is not periodic, the frequency domain analysis filters it out.
In
In
In
In
The housing 1 in
While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.
