GB2392501A

GB2392501A - Meter condition monitoring device

Info

Publication number: GB2392501A
Application number: GB0220109A
Authority: GB
Inventors: Lawrence Martyn Wallis; Mark Robert Burrows
Original assignee: Lattice Intellectual Property Ltd
Current assignee: Lattice Intellectual Property Ltd
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-03
Anticipated expiration: 2022-08-30
Also published as: GB2392501B; GB0220109D0

Abstract

A condition monitoring device 1 for a rotary positive displacement meter 5. The device comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the gas meter and a connection to a pulse output on the gas meter. A gas meter fitted with the device and a method of monitoring gas meter operation are also claimed. The condition monitoring device measures the pressure differential across the gas meter, and also detects a pulsating output therefrom. The processor then uses the measured values to make comparisons to predetermined ideal values so as to ascertain the condition of the meter.

Description

PRIORITY SPECIFICATION

Title: Meter Condition Monitoring Device This invention relates to a meter condition monitoring device (MCMD), to a method of monitoring the operation of a rotary positive displacement gas meter (RPD) using the device and to an (RPD) gas meter fitted with the device.

Rotary positive displacement gas meters (RPD) are commonly in use in the gas supply industry. A typical (RPD) contairis a pair of moveable flanges or impellers which rotate, allowing gas under pressure to pass through the meter. Variations in the pulses of gas across the impellers can indicate problems with the meter. In particular the pressure differential (PD) of the gas supplied to the meter increases as the meter grows older. In conventional operation of (RPD) the (PD) is routinely monitored and compared with a table of values to determine when the meter is about to become faulty and needs to be serviced. There is however a need to monitor other parameters in addition to (PD) in order to ascertain fully the effectiveness of an (RPD). Such monitoring or "health check" of an (RPD) should be done without the need for removing the meter from the line or interrupting the gas supply.

According to the present invention we provide a meter condition monitoring device (MCMD) to monitor a rotary positive displacement gas meter (RPD) which comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the (RPD) and a connection to a pulse output on the (RPD).

Further according to the invention we provide a method of monitoring the operation of a rotary positive displacement gas meter (RPD) in which the operation is monitored using a meter condition monitoring device (MCMD) which comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the (RPD) and a connection to a pulse output on the (RPD) Further according to the invention we provide an (RPD) gas meter, fitted with a meter condition monitoring device (MCMD) which device comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the (RPD) and a connection to a pulse output on the (RPD).

Preferably, the (MCMD) is designed to monitor the (RPD) to ensure that it operates within suitable parameters for example to provide a degree of protection at least equal to the standards of {P65.

The IP rating system is used to indicate the degree of protection provided by enclosures for use in demanding or hostile environments.

The current design of the Condition Monitoring (CMD) unit enclosure is to IP65. The first digit (6) indicates the protection against solid matter (dust etc). The second digit (5) indicates protection against liquids. The protection of the CMD is: Solid protection 6 = "Complete protection against contact with live or moving parts inside the enclosure. Protection against ingress of dust".

Liquid protection 5 = "Protection against water jets: Water projected by a nozzle from any direction shall have no harmful effect" Suitably the (MCMD) is designed to be used within hazardous areas to the extent which is necessary in any given application.

Most modern (RPD) meters are fitted with low frequency (LF) pulse outputs by their manufacturers. An (LF) pulse output is an electronic switch which gives an electrical pulse output as the meter gearing turns. This pulse may be used by data logging equipment etc. to calculate flow rates.

Manufacturers supply (LF) pulse information and it is possible to calculate the number of pressure pulsations that are to be expected from a particular model of meter. Using this, the (MCMD) can calculate flowrates and can also alert an operator to error conditions if the number of (LF) pulses and pressure pulsations do not agree.

The (MCMD) of the invention is designed to perform a "health check" on an (RPD) by monitoring a number of parameters including (PD) across the meter without the need for removing the meter from the line or interrupting the gas supply. It is designed to perform a number of computations to determine the various meter failures that may occur including the following: 1. it uses the pressure pulsations generated by meter impellers (flanges) to determine the speed of rotation of the meter and thereby to determine the flowrate at which the meter is running.

2. It uses the flowrate determined in (1) above to calculate the (PD) that a properly operating or healthy meter would have at that flowrate and then compares it with the (PD) that it measures, thereby determining the health of the bearings and of the measuring chamber of the (MCMD).

3. It monitors the number of pressure pulsations generated by the meter's impellers per pulse if the number of pulses is constant and compares it with the number that should occur for that type of meter. If the number of pressure pulsations occurring within the period of one LF pulse varies by more than a preset tolerance then a fault is held to exist. This determines whether an index fault or a fault in the magnetic coupling has occurred.

s 4. It logs the transient differential pressure characteristic that is generated as the meter starts and then calculates the flowrate from the first 8 seconds of pressure oscillation data. Comparing the measured | pdt with a predetermined relationship of pat against the flowrate for 8 seconds pressure oscillations enables the device to determine the health of the bearings and measurement chamber.

5. The device is capable of logging either when faults are suspected and/or logging the actual characteristics of the (RPD).

6. The algorithms and limits used do not apply when a pressure pulsation resonance is generated by the meter. To overcome this problem the (MCMD) puts the results into flow bands. If all of the faults occur in a certain flow band and the, meter is apparently healthy at all other flows and on start up, then these results will be ignored. The device can be fitted with a power source to enable it to operate for a considerable period, e. g. up to a year. This makes it very flexible in operation. It can be left in place for a day to give a quick result or for up to a year. Different problems may occur at different gas flowrates, so monitoring the (RPD) for a longer period will give information of performance at many flows.

The invention is illustrated by the following drawings wherein: Figure 1 is a schematic diagram of the device attached to an (RPD).

Figure 2 is a sketch of part of an (RPD) showing the moveable flange impellers.

Figure 3 is a graph produced by a meter running (PD)/LF test determined in numbered computation 1 above.

Figure 4 is a graph of a start-up test produced as described in numbered computation 3 above.

Figure 5 is a graph of integral area plotted against flowrate for a number of meters illustrating numbered computation 4 above.

Figure I shows an (MCMD) 1 connected by pressure connections 2 and 3 and by electrical connection 4 to (RPD) meter 5. (MCMD) 1 is also connected by electrical connection 6 to computer 7 which controls it and receives data regarding the performance of (RPD) 5 enabling this to be monitored.

Figure 2 shows a detail of an (RPD) 5 as shown in Figure 1. This has a meter body 8 with inlet connection 9 and outlet connection 10 to gas flow pipe 11. Gas flow is in the direction shown by the arrow. Inside meter body 8 are moveable flange impellers 12 and 13 which in operation rotate about their axes to open and close holes admitting or releasing pulses of gas to or from the (RPD). Variations in these pulses are recorded using (MCMD) 1 of Figure I and enable the performance of (RPD) 5 to be monitored.

Figure 3 is a diagram showing the relationship between (LF) pulses and meter pressure pulses. The meter 5 gives an (LF) pulse for a predetermined rotation of the À meter gearing. Each rotation of meter 5 will produce four pressure pulsations. Each impeller (12, 13) causes two peaks and there are two impellers.

Figure 4 shows startup test pressure pulsations. The (MCMD) I logs the differential pressure characteristic as the (RED) 5 starts and compares this with a predetermined relationship |pdt against the flowrate. The graphic in Figure 4 shows that as (RPD) 5 starts, there is a large pressure pulse that decays in a short period of time, before reaching a settled constant value.

Initially (MCMD) 1 was designed to calculate flowrate based on the first 20 pressure pulsations. Later, however, it was redesigned to calculate the value based on the entire sampling period. This gives a more reliable result.

Figure 5 displays startup results for nine different meters. The test was conducted as described above in relation to Figure 4. The predetermined relationship is shown as the straight dotted line in the graph. Any meter lying below this line is deemed to be "healthy", and any above the line is taken as "unhealthy".

Claims

1. A meter condition monitoring device to monitor a rotary positive displacement gas meter which comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the gas meter and a connection to a pulse output on the gas meter.

2. A meter condition monitoring device according to claim I which comprises a microprocessor having two inputs.

3. A method of monitoring the operation of a rotary positive gas meter in which the operation is monitored using a meter condition monitoring device which comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the gas meter and a connection to a pulse output on the gas meter.

4. A rotary positive gas meter fitted with a meter condition monitoring device, which device comprises a microprocessor circuit having at least two inputs, a differential pressure transducer which can be connected across the gas meter and a connection to a pulse output on the gas meter.