GB2253102A

GB2253102A - Analogue signal monitoring unit

Info

Publication number: GB2253102A
Application number: GB9103667A
Authority: GB
Inventors: Peter Rodney Maddock
Original assignee: C & I Consultants Ltd
Current assignee: C & I Consultants Ltd
Priority date: 1991-02-21
Filing date: 1991-02-21
Publication date: 1992-08-26
Also published as: GB9103667D0

Abstract

An analogue signal monitoring unit 1 monitors one or more variable analogue signals indicative of a process to be monitored, for example the emissions from a coal-fired power generation plant. The unit 1 comprises an input for receiving the process signals, an analogue-to-digital converter which samples the signals every ten seconds and sequentially outputs digital sample signals to a processing circuit which calculates four different average values indicative of the process monitored, and a digital-to-analogue converter average outputting signals to a chart recorder. The processing circuit provides a ten minute rolling average, a two hour rolling 3 average, a calendar month average and a 720 hour average 6 which may be indicated on a display 3. <IMAGE>

Description

"Analogue Signal Monitoring Units" This invention relates to analogue signal monitoring units for monitoring one or more variable analogue signals indicative of a process to be monitored.

There are many applications in which variable analogue signals from process instrumentation require to be monitored under different conditions of operation of the process. Such monitoring may require both a continuously updated indication of the current state of the process and a-cumulative indication of the state of the process over an extended interval of time. For example, environmental control of emissions from a coal-fired power generation plant requires monitoring of the flue gases, both when the plant is on load and when the plant is off load, on a continuous basis and also over an extended period of time.

It is an object of the invention to provide a novel analogue signal monitoring unit which is particularly adapted to provide meaningful monitoring of process signals under such conditions.

According to the present invention there is provided an analogue signal monitoring unit for monitoring one or more variable analogue signals indicative of a process to be monitored, comprising input means for receiving the or each analogue signal, sampling means for sampling the or each analogue signal at a predetermined sampling rate and for sequentially outputting digital sample signals indicative of the sampled values, and first averaging means for receiving the sample signals and for producing from the sample signals a first rolling average signal which is indicative of the average of the sample signals received over an immediately preceding interval of time of a first predetermined duration and which is sequentially updated on receipt of further sample signals.

Furthermore it is preferred that the unit further comprises control input means for receiving one or more control signals, and averaging control means for controlling averaging of the sample signals in dependence on the control signals received. For example the averaging control means may be adapted to inhibit averaging of the sample signals on receipt of a calibrating signal indicating that calibration of instrumentation used in the process being monitored is taking place.

The unit may also include second averaging means for receiving the sample signals and for producing from the sample signals a second rolling average signal which is indicative of the average of the sample signals received over an immediately preceding interval of time of a second predetermined duration longer than said first duration and which is sequentially updated on receipt of further sample signals. The first duration may be ten minutes, and the second duration may be two hours, for example.

The second averaging means may be arranged to average the sample signals under control of the averaging control means only when the control signals indicate a first operational state of the process being monitored, such as an on-load condition, and not when the control signals indicate a second operational state of the process being monitored, such as an off-load condition.

The unit may also include third averaging means for receiving the rolling average signals produced by the first and/or second averaging means and for producing from the rolling average signals an average signal which is indicative of the average of the first and/or second rolling average signals over an interval of time of a third duration longer than said first and/or second durations. The third duration may be a calendar month, and the average signal may be an average of the two-hour rolling average signals received in a month while the process is on load, for example.

The unit may additionally include fourth averaging means for receiving the rolling average signals produced by the first and/or second averaging means and for producing from the rolling average signals a further average signal which is indicative of the first and/or second rolling average signals over an interval of time of a fourth duration longer than said first and/or second durations. The fourth duration may be 720 hours, for example.

The unit preferably includes digital display means for displaying the signals produced by the averaging means, and indexing means for selecting the signals to be displayed by the display means from amongst a plurality of signals which can be displayed. The display means may comprise two display devices which normally display the first and second rolling average signals respectively.

Furthermore the unit may include output means for outputting one or more analogue signals indicative of the first and/or second rolling average signals to recording means.

In order that the invention may be more fully understood, a preferred form of monitoring unit in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of the housing of the unit; Figure 2 is an overall schematic diagram of the unit; Figure 3 is a functional block diagram of the unit.

Referring to Figure 1 the monitoring unit 1 has a housing 2 having a display 3 and a push button 4. The display 3 comprises two three digit, seven segment light-emitting diode display units 5 and 6 for respectively displaying a ten minute rolling average signal and a two hour rolling average signal on a continuous basis under normal monitoring conditions. The housing 2 is suitable for mounting in an equipment rack or on a control desk, and has terminals (not shown) at its rear for supply of power and for inputting and outputting of signals.

The push button 4 may be pressed to provide a number of temporary indications on the display 3, each indication being shown for fifteen seconds (provided the push button is not pressed again in that period) before the two display units 5 and 6 are again caused to display the ten minute and two hour rolling average signals. If the push button 4 is pushed only once both of the display units 5 and 6 provide an indication "888" as a lamp test facility. If the push button 4 is pressed more than once in sequence the display unit 5 is caused to indicate one of the sequence numbers shown below whilst the other display unit 6 is caused to show values indicative of the data shown below against these sequence numbers.

1. Calendar month average to date 2. Average for last calendar month 3. 720 hour average to date 4. 720 hour average for last period 5. Hours logged to date for 720 hour average 6. Date of start of 720 hour average 7. Month of start of 720 hour average 8. Year of start of 720 hour average 9. Hour of start of 720 hour average 10. Minutes of start of 720 hour average Referring to Figure 2 the unit 1 has an input 10 for receiving analogue signals of 0-20mA, being for example the output signals of transducers for measuring the emissions from a coal-fired power generation plant.

Furthermore the unit 1 has a control input 11 for receiving digital signals indicating whether the process instrumentation is calibrating and also whether the state of the process is on load or off load. The analogue signals received at the input 10 are supplied to an analogue to digital converter 12 which samples the signals every ten seconds, and sequentially outputs the resulting digital sample signals to a processing circuit 13. The digital signals received at the control input 11 are supplied to a control circuit 14 which controls the processing of the digital sample signals so that sample values taken while the process instrumentation is calibrating are ignored, and so that the two hour rolling average value is calculated only when the process is on load. It will be appreciated that the processing circuit 13 may be constituted either by a series of discrete circuit components or by a suitably programmed microprocessor.

The processing circuit 13 is adapted to calculate four different average values indicative of the process monitored, as follows: 1. A ten minute rolling average indicative of the average of the sample signals received over an immediately preceding ten minute interval, this value being updated on receipt of a further sample signal every ten seconds.

2. A two hour rolling average indicative of the average of the sample signals received over an immediately preceding two hour interval while the process is on load, this value being updated on receipt of a further sample signal every ten seconds.

3. A calendar month average calculated from the two hour rolling averages determined while the process is on load during a period of a calendar month.

4. A 720 hour average calculated from the two hour rolling averages over a period of 720 hours of operation of the process.

The rolling averages are not only indicated on the display 3 but are also supplied to a digital to analogue converter 15 for outputting 0-20mA output signals from an output 16 to a chart recorder. Furthermore a universal asynchronous receiver/transmitter (UART) 17 outputs digital signals from a RS232 output 18 to enable the unit to download data to a printer or computer system.

The unit may be adapted to calculate the averages of either one signal or two signals received at the input 10 depending on the setting of internal setting switches. Furthermore the averaging periods and the control logic may be altered by suitable programming and/or circuit design to enable adaptation of the unit to different monitoring requirements and different operating conditions.

Figure 3 indicates diagrammatically the manner in which the input signals are received and sampled and the manner in which the sample signals are processed to produce the ten minute rolling average, two hour rolling average, calendar month average and 720 hour average signals.

Claims

1. An analogue signal monitoring unit for monitoring one or more variable analogue signals indicative of a process to be monitored, comprising input means for receiving the or each analogue signal, sampling means for sampling the or each analogue signal at a predetermined sampling rate and for sequentially outputting digital sample signals indicative of the sampled values, and first averaging means for receiving the sample signals and for producing from the sample signals a first rolling average signal which is indicative of the average of the sample signals received over an immediately preceding interval of time of a first predetermined duration and which is sequentially updated on receipt of further sample signals.

2. A unit according to Claim 1, which further comprises control input means for receiving one or more control signals, and averaging control means for controlling averaging of the sample signals in dependence on the control signals received.

3. A unit according to Claim 2, wherein the averaging control means is adapted to inhibit averaging of the sample signals on receipt of a calibrating signal indicating that calibration of instrumentation used in the process being monitored is taking place.

4. A unit according to Claim 1, 2 or 3, which includes second averaging means for receiving the sample signals and for producing from the sample signals a second rolling average signal which is indicative of the average of the sample signals received over an immediately preceding interval of time of a second predetermined duration longer than said first duration and which is sequentially updated on receipt of further sample signals.

5. A unit according to Claim 4 when appended to Claim 2 or 3, wherein the second averaging means is arranged to average the sample signals under control of the averaging control means only when the control signals indicate a first operational state of the process being monitored, and not when the control signals indicate a second operational state of the process being monitored.

6. A unit according to any preceding claim, which includes third averaging means for receiving the rolling average signals produced by the first and/or second averaging means and for producing from the rolling average signals an average signal which is indicative of the average of the first and/or second rolling average signals over an interval of time of a third duration longer than said first and/or second durations.

7. A unit according to Claim 6, which includes fourth averaging means for receiving the rolling average signals produced by the first and/or second averaging means and for producing from the rolling average signals a further average signal which is indicative of the first and/or second rolling average signals over an interval of time of a fourth duration longer than said first and/or second durations.

8. A unit according to any preceding claim, which includes digital display means for displaying the signals produced by the averaging means, and indexing means for selecting the signals to be displayed by the display means from amongst a plurality of signals which can be displayed.

9. A unit according to Claim 8 when appended directly or indirectly to Claim 4, wherein the display means comprises two display devices which normally display the first and second rolling average signals respectively.

10. A unit according to any preceding claim, which includes output means for outputting one or more analogue signals indicative of the first and/or second rolling average signals to recording means.

11. An analogue signal monitoring unit for monitoring one or more variable analogue signals indicative of a process to be monitored, the unit being substantially as hereinbefore described with reference to the accompanying drawings.