GB2216313A

GB2216313A - Control apparatus

Info

Publication number: GB2216313A
Application number: GB8903394A
Authority: GB
Inventors: Sean Giblin; John Bryne; Naveen Goswami
Original assignee: BEMSTECH Ltd
Current assignee: BEMSTECH Ltd
Priority date: 1988-02-19
Filing date: 1989-02-15
Publication date: 1989-10-04
Also published as: IE880452L; ZA891142B; IE61163B1; GB8903394D0

Abstract

An outstation control device (3) for controlling e.g. temperature at a number of locations in a building is networked to a plurality of other outstation control devices (3) and a personal computer. Each outstation control device (Fig. 2) comprises a central processing unit (4), an analog signal delivering device (8), a memory and clock card (12) and a communications processor (19). The device (6) receives analog signals from temperature sensors, inside and outside the building for delivery to the central processing unit (4) after amplifying (40) them with continually updated gain and offset. The device (8) delivers signals under the control of the central processing unit (4) to operate valves, boilers and the like for controlling the temperature of the location. The communications processor (19) communicates with the personal computer and other devices (3) through ports (22, 23) using RS 232 and RS 422 Protocol respectively, and is connected to the central processing unit (4), the memory and clock card (12) and the devices (6) and (8) by a serial data link (20) to speed up communications within the control device (3). <IMAGE>

Description

TITLE: - Control Apparatus The present invention relates to control apparatus and in particular to control apparatus for controlling a parameter of a building or location in a building or other compound, an example of such a parameter being temperature humidity and the like. The invention also relates to an outstation control device for controlling a parameter in a location of the building and to a method for controlling temperature in the building and/or location in the building.

According to the invention, there is provided an outstation control device for controlling a parameter of a building or compound, the outstation control device comprising a central processing unit for controlling the operation of the device, an analog signal receiving device for receiving a plurality of inputs corresponding to the value or values of the parameter in the building for communicating to the central processing unit, an analog signal delivering device for delivering a signal from the central processing unit to apparatus for controlling the parameter, the central processing unit, analog signal receiving device and analog signal delivering device being connected, and communicating means for communicating the outstation control device with a central computer, wherein the communicating means comprises a communications processor, the communications processor, the central processing unit, the analog signal receiving device and the analog signal delivering device being connected through a synchronous data link.

Preferably, the communications processor of each outstation control device communicates with the central computer through a serial port or ports. Advantageously, each outstation control device comprises a memory and clock card connected into the synchronous data link.

In one embodiment of the invention, the communications processor, the central processing unit, the analog signal receiving device and the analog signal delivering device and the memory and clock card are each provided as a single card.

Further, the invention provides control apparatus for controlling a parameter at a number of locations in a building or compound, the control apparatus comprising a plurality of outstation control devices according to the invention, one for each location, for controlling apparatus for varying the parameter of the location, the outstation control devices being connected in a network, and a central computer in the network communicating with the outstation control devices.

Additionally, the invention provides a method for controlling the temperature of a location in a building using an outstation control device according to the invention, the method comprising the steps of monitoring the temperature inside and outside the building, computing the temperature gain constant and temperature loss constant of the building from the monitored data, computing the optimum start and stop times of apparatus for varying the temperature of the building in response to the monitored temperatures and computed constants and selecting a set of output signals from the look up table in the memory and clock card corresponding to the computed temperature values, and delivering the set of signals to the apparatus for controlling the temperature of the building through the analog signal delivering device.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a block representation of control apparatus according to the invention, Fig. 2 is a block representation of a outstation control device also according to the invention for use in the control apparatus of Fig. 1, Fig. 3 is a flow chart of a programme for use with the control apparatus of Fig. 1, Fig. 4 is a flow chart of another programme also for use with the control apparatus of Fig. 1, Fig. 5 is a flow chart of another programme for use in the control apparatus of Fig. 1, Fig. 6 is a flow chart of another progrmme for use in the apparatus of Fig. 1.

Referring to the drawings and initially to Figs. 1 and 2, there is illustrated a block representation of control apparatus according to the invention indicated generally by the reference numeral 1 for controlling parameters in this case temperature and lighting in a plurality of locations in a building (not shown). The control apparatus 1 comprises a plurality of outstation control devices 3 also according to the invention for controlling the parameters in the locations, one device 3 for each location. The outstation control devices 3 are networked and a central computer, namely a personal computer 2 is connected into the network for controlling the outstation control devices 3. Each outstation control device 3 is illustrated in Fig. 2.While the control apparatus controls the lighting of the building and the temperature of the building, its main function is to control the temperature, and by accurately controlling the temperature the energy requirement for heating the building is reduced. Accordingly, it is intended here, as well as describing the apparatus, to describe only the function of the apparatus in controlling the temperature of the building. Once the operation of the control apparatus in controlling the temperature of the building is understood, the control of other parameters will be readily apparent to those skilled in the art.

Each outstation control device comprises a central processing unit 4 which controls the operation of the outstation control device 3. An analog signal receiving device 6 in the outstation control device 3 receives signals from a plurality of monitors appropriately located in the location of the building to be controlled by the device 3. In this case, the analog signal receiving device 6 has sixteen input channels 7 for receiving signals from sixteen monitors. The monitors (not shown) include temperature sensors for monitoring temperature and other sensors for monitoring other parameters in the location. The temperature sensors are provided inside and outside the building for monitoring inside and outside temperatures.The input channels 7 can each receive an analog signal of from 0 to 10 volts and from 4 to 20 milliamps, such a signal would be provided from a temperature sensor and the like or a passive thermistor type sensor. An analog signal delivering device 8 in the outstation control device 3 comprises sixteen output channels 10 for delivering output signals under the control of the central processing unit 4 as will be described below to various apparatus for controlling the temperature and other parameters of the location in the building, for example, valves of central heating system, pumps, boilers, light switches and the like, none of which are shown. Each channel 10 can deliver a signal of from 0 to 10 volts and 4 to 20 milliamps for positioning a valve actuator, acutating a pump, central heating boiler, switch, relay and the like.

A memory and clock card 12 in the outstation control device 3 comprises a real time clock 14 for clocking the input and output signals and delivery of data. The memory and clock card also comprises a read only memory 15 and a random access memory 17. The read only memory 15 stores the computer programmes for reading and writing the input and output signals to and from the devices 6 and 8 and for computing the parameters and other data as will be described below necessary for the control of the parameters of the location in the building. An address decoder 18 is also provided in the memory and clock card 12. The memory and clock card are provided as a single card.

A communications processor 19 which handles communications between the outstation control device 3 and the central computer 2 and other outstation control devices 3 is also provided in the outstation control device 3. In this case, the communications processor 19, the central processing unit 4, the analog signal receiving device 6 and the analog signal delivering device 8 and the memory and clock card 12 are connected by a synchronous data link 20. The communications between the communications processor 19 and the network and the central computer 2 are through a pair of serial ports 22 and 23 from the communications processor 19. The port 22 is a supervisor port for connection to the central computer 2 and communicates with the central computer 2 using RS 232 Communications Protocol.The port 23 communicates with the other outstation control devices 3 in the network using RS 422 Communications Protocol. In this case, only one of the outstation control devices, namely the device 3a communicates directly with the computer 2.

Communications between the computer 2 and the other outstation control devices 3 are handled through the communications processor 19 of the outstation control device 3a. By virtue of the fact that the synchronous data link 20 is used for connecting the communications processor 19, the central processing unit 4, the analog signal receiving and delivering devices 6 and 8 and the memory and clock 12, the communications within each outstation control devices 3 are considerably enhanced and speeded up. Thus, delays which would otherwise occur in communicating with the central computer 2 are eliminated.

The communications processor 19 comprises a microprocessor 25 which controls the operation pf the communications processor 19. A read only memory 26 stores the programme for controlling the microprocessor 25 for communication.

A random access memory 27 stores data to be transferred to the central computer 2 by the communications processor 19.

Data received for transmission to the central processing unit 4 of the outstation control device 3 is also stored in the random access memory 27. Synchronous communication interface adaptors 29 and 30 control the serial ports 22 and 23 respectively. A buffer 31 controls the transfer of data between the communications process 19 and the synchronous data link 20. The communications processor is provided by a single card.

The central processing unit 4 comprises a microprocessor 33 which controls the operation of the central processing unit 4 and the operation of the outstation control device 3. A read only memory 34 stores the programmes for controlling the microprocessor 33 and the programmes for reading inputs from the analog signal receiving device 6 and for writing output signals to the analog signal delivering device 8. A random access memory 35 stores and holds data and parameters read and to be written. An address decoder 36 and control logic unit 37 will be well known to those skilled in the art. The central processing unit uses a page address system allowing it to address up to 304 Kbytes of memory. The central processing unit 4 is provided by a single card.

The analog signal receiving device comprises a multiplexer 39 for receiving the parallel analog signals on the sixteen channels and multiplexing them into serial signals for delivery to a DC amplifier 40. The amplified signals from the amplifier 40 are delivered to an analog to digital converter 41 from which they are delivered through a data bus onto the synchronous data link 20 for delivery to the central processing unit 4. An address decoder 42 is also provided in the analog signal receiving device.

The offset and gain of the amplifier 40 are varied by an offset control circuit 43 and a gain control circuit 44 respectively. The circuits 43 and 44 vary the offset and gain depending on the source from which the signal on the input channels 17 is being read. The offset and gain are varied under the control of the central processing unit 4 under the control of software stored in the read only memory 34 to match the monitoring unit (not shown) from which the signal is being read. The analog signal receiving device is provided by a single device.

The analog signal delivering device 8 comprises a digital to analog converter 45 for converting the signal received from the central processing unit 4 into an analog signal.

A multiplexer 46 delivers the data from the digital to analog converter 45 onto the output channels 10 for delivering to the various apparatus for controlling the parameters. A sample and hold circuit 47 is provided on each output channel 10 of the device 8. A decoder 48 is provided in the device 8. The analog signal delivering device is provided by a single device.

During set up of the system, the gains and offset associated with each of the sensors connected to the input channel 7 of the device 6 of each outstation control device 3 are entered into the central computer 2 and downloaded to the appropriate outstations 3. Various other required data which will be well known to those skilled in the art is likewise entered into the central computer for downloading to the appropriate outstation 3 during set up. The temperature at which each location of the building is to be maintained and the time period within which it is to be maintained at the desired temperature are similarly entered into the central computer 2 and are subsequently downloaded to the appropriate outstations 3. Similarly, the lighting requirements of the various locations of the building are also entered through the computer 2.

The operation of the control apparatus 1 will now be described.

Referring to Fig. 3, the flow chart of a programme for reading the values of the sensors connected to the input channels 7 of the analog signal receiving device 6 is illustrated. Block 50 of the flow chart writes the appropriate gain and offset of the amplifier 40 to the gain and offset circuits 44 and 43 respectively of the device 6. The values of the gain and offset written are matched to the sensor connected to the input channel 7 from which the signal is being read. The gains and offsets for each sensor are stored in a look-up table in the random access memory 35 of the central processing unit 4. Block 50 also selects the analog input channel 7 which is to be read by writing the input number of the sensor to the multiplexer 39. The gain and offset is again written to start the conversion. Block 50 also reads the byte from the analog to digital converter 41 after 20 microseconds. Block 51 repeats steps II and III of block 50 eight times and gets an average value for each set of eight readings from each channel 7. Block 52 feeds the average value through an exponential filter (not shown) to the central processing unit 4. Block 53 rescales the read value of the input to the engineering value. Block D4 stores the value in an input output table in the random access memory 35 of the central processing unit 4. This procedure is carried out until all the values from the various sensors on the input channel 7 to the analog signal receiving device 6 have been read.

The flow chart of Fig. 4 is of a programme for writing the signal value for delivery through the analog signal delivering device 8 to the appropriate apparatus for controlling the temperature of the building. Block 60 gets the value of the signal to be written to the device 8 on the appropriate output channel 10 from an input output table in the random access memory 35 of the central processing unit 4. Block 61 selects the output channel 10 on the multiplexer on which the multiplexer is to deliver the signal. Block 62 converts the output signal from 0% to 100% to O to 255 bytes so that the output signal sets the apparatus to be controlled at the appropriate position or setting. Block 53 writes the value of the signal prepared by block 52 to the digital to analog converter 45 of the device 8.

A control loop controls the output signals which are to be delivered onto the channels 10 of the device 8 based on the input signals received on the input channels 7 of the device 6. Various computations are carried out in the control loop. The flow chart illustrated in Fig. 5 illustrates the order in which the computations which are carried out in the control loop. The control loop controls the measured value, namely the process variable to the selected set point of the temperature. The control can be proportional, proportional plus integral or proportional plus integral plus derivative to give the best response. These control loops can be cascaded to provide relatively complex control strategies.In this case, a proportional plus integral plus derivative loop for determining output values from the process variable and desired set point will be described with reference to the flow chart of Fig. 5. Block 70 of the flow chart obtains the process variable value from an input output table from the random access memory 35 of the central processing unit 4. Block 71 gets the set point value from a control loop parameters list which is stored in a look-up table in the random access memory 17 of the memory and clock card 12. For the heating circuit the set point is a medium temperature value which is determined. using the optimiser described below. Block 72 obtains the medium temperature value. Block 73 gets the proportional plus integral plus derivative constants from the control loop parameters list in the look-up table in the random access memory 17.Block 74 calculates the error by subtracting the process variable from the set point value.

Block 75 integrates the error and adds the value to the integral term. Block 76 differentiates the error and adds the result to the derivative term. Block 77 calculates the output which is equal to the gain by the error plus the integral term minus the derivative term. Block 78 limits the output between 0% and 100,0. Block 79 puts the output value in the input/output table in the random access memory 35 of the central processing unit 4.

The optimum time for stopping and starting the various apparatus which control the parameters of the location in the building is carried out by using optimum start and stop times. These optimum start and stop times are stored in the random access memory 35 of the central processing unit 4. The optimum start and stop times are continuously updated as the temperature gain and temperature loss characteristics of the building vary. These gains and losses are continuously updated from the inputted data received on the input channels 7 of the analog signal receiving devices 6. As a result of changes in the temperature gain and temperature loss characteristics, the values of the output signals stored in the look-up tables in the random access memory 35 of the central processing unit 4 against temperature values are altered.This therefore optimises the heating and cooling start and stop times which in turn minimises the running time of the apparatus for maintaining the temperature of the location in the the building. Each stored signal also has a corresponding weather compensator which achieves the required conditions by predicting the medium temperature according to the variation in outside temperature.

Fig. 6 illustrates a flow chart of a programme for starting up and shutting down the heating plant of a building or location in the building using the optimum start and stop times. Block 80 of the flow chart obtains the inside temperatures of the location in the building, the outside temperature and the medium temperature from the appropriate look-up table in the random access memory 35 of the central processing unit 4. The occupancy period for the building is stored in a weekly time schedule which is stored in the random access memory 17 of the memory and clock card 12. Block 81 obtains the occupancy period from the random access memory 17. Block 82 checks if it is time to optimum start. If it is, then the heating plant is started. Block 82 also calls up a data accumulator mode routine for updating the building temperature gain and temperature loss constants.Block 83 checks if the time is during occupancy period and checks if the heating is required and if the heating plant is off. If the answer to all three is yes, then the heating plant is started. Block 84 checks if the time is after the occupancy period and if the time is before the optimum stop time. If so, the weather compensator value is calculated for the medium temperature as a function of the outside and inside temperature. Block 85 checks if it is time for the optimum stop, and if so, the heating plant is stopped. Block 85 also calls up the data accumulating mode routine for updating the building temperature loss constant.

The calculations carried out by the programme of Fig. 5 are based on the following theory.

Newton's First law of cooling dTi --- = Cg (Tm - Ti) - C1 (Ti - To) Heating/Cooling Loss Term where Ti = inside temperature Tm = medium temperature To = outside temperature g = gain constant C1= loss constant t = time.

Cg and C1 are degC/Unit Time per degC temperature difference, This rate equation is the energy balance for a building.

In other words, the rate of change of energy = heat in flux - heat out flux.

By solving the First order linear differential equation above, the Optimum Start and Stop Times can be derived.

The time taken to achieve a target inside temperature Ti(t) from the initial inside temperature Ti(O) is 1 Ti(t) - K ts = - --------- x ln (------------) Cg+C1 Ti(O) - K where K = (C1 x To + Cgx Tm) / (C + C g g The time taken to cool down to a target inside temperature Ti(t) from the initial inside temperature Ti(O) is 1 Ti(t) - T t = - ---- x In ) P C1 Ti(O) - To The weather compensator computes the required medium temperature for a desired inside temperature given an outside temperature using Newton's first law of cooling set out above.Since a stable inside temperature is required dTi = O dt therefore C (Tm - Ti) = Ci (Ti - To) g 1 or C1 Tm = -- (Ti - To) + Ti Cg Ti is the desired inside temperature.

The computer medium temperature is then maintained by the proportional plus integral plus derivative loop, controlling the medium temperature. If, however, the inside temperature goes to either too low a value or too high a value, the medium temperature is compensated to achieve the desired inside temperature.

The advantages of the invention are many and one of the most important advantages achieved by the invention is that data can be readily quickly transmitted between the communications processor and the other cards connected to the synchronous data link, thus avoiding undue delays which would otherwise occur. Another important advantage of the invention is achieved by virtue of the fact that the apparatus by continuously monitoring the temperature of the building during heating up and cooling down and using these monitored results for updating the gain and loss constants, the start up and shut down times can be optimised.

It will, of course, be appreciated that while the analog signal receiving and delivering devices have been described as each comprising sixteen channels, they could be provided with any number of channels greater or lesser.

Further, it will be appreciated that all sixteen channels in all cases won't be used for monitoring temperature or controlling heating apparatus, for example, some of the channels could be used for monitoring the light level in the building, and for switching on and off the lights, while other input and output channels respectively could be used for monitoring humidity and controlling apparatus for varying the humidity.

Claims

1. An outstation control device for controlling a parameter of a building or compound, the outstation control device comprising a central processing unit for controlling the operation of the device, an analog signal receiving device for receiving a plurality of inputs corresponding to the value or values of the parameter in the building for communicating to the central processing unit, an analog signal delivering device for delivering a signal from the central processing unit to apparatus for controlling the parameter, the central processing unit, analog signal receiving device and analog signal delivering device being connected, and communicating means for communicating the outstation control device with a central computer, wherein the communicating means comprises a communications processor, the communications processor, the central processing unit, the analog signal receiving device and the analog signal delivering device being connected through a synchronous data link.

2. An outstation control device as claimed in Claim 1 in which the communications processor is provided with a serial port or ports for communicating with the central computer.

3. An outstation control device as claimed in Claim 1 or 2 in which the communications processor is provided with a serial port for communicating with other outstation control devices in a network.

4. An outstation control device as claimed in any preceding claim in which a memory and clock card is connected into the synchronous data link.

5. An outstation control device as claimed in any of Claims 1 to 4 in which the analog signal receiving device comprises a plurality of input channels for receiving a plurality of inputs in respect of the parameter or parameters being monitored, a multiplexer for multiplexing the parallel received signals into a serial signal, and an analog to digital converter for receiving the serial signal from the multiplexer.

6. An outstation control device as claimed in Claim 5 in which the offset and gain of the amplifier of the analog signal receiving device is variable under the control of the central processing unit.

7. An outstation control device as claimed in any preceding claim in which the analog signal delivering device comprises a plurality of output channels for delivering signals to a plurality of apparatus for varying the parameter or parameters, a multiplexer for converting a serial signal into a parallel signal for delivering to the output channels, and a digital to analog converter for converting the digital signals fed from the central processing unit to analog signals for delivering to the multiplexer.

8. An outstation control device as claimed in any preceding claim in which the central processing unit comprises a microprocessor for controlling the operation of the outstation control device, a read only memory for storing the programmes for reading the inputs from the analog signal receiving device and writing outputs to the analog signal delivering device, a random access memory for temporarily storing data to be transferred to the central processing unit, and an address decoder for controlling the inputs and outputs being read and written to the analog signal receiving and delivering devices.

9. An outstation control device as claimed in any preceding claim in which the communications processor comprises a microprocessor for controlling the operation of the communications processor, a read only memory for storing the programme to control the microprocessor for communications, a random access memory for storing data to be transferred from the outstation control device to the central computer, a buffer for directing data on the synchronous data link, and at least one synchronous communications interface adaptor for delivering data in serial form from the communications processor to the central computer.

10. An outstation control device as claimed in any of Claims 4 to 9 when dependent on Claim 4 in which the memory and clock card comprises a real time clock for clocking the transfer of data on the synchronous data link, a read only memory for storing programmes for carrying out computations, a random access memory for storing data to be operated on by the programme in the read only memory of the memory and clock card, and an address decoder.

11. An outstation control device as claimed in any preceding claim in which the parameter to be controlled is the temperature of the building or compound, reference temperature values being stored in look-up tables in the random access memory of the clock card, values of sets of output signals for delivery through the analog signal delivering device being stored in the look-up tables of the random access memory, each set of output signals corresponding to a reference temperature value, the microprocessor of the central processng unit comprising means to compute the temperature of the building under the control of the programme in the read only memory of the memory and clock card from the input signals received by the analog signal receiving device, and means to select a set of stored output signals from the look-up tables corresponding to the computed temperature value of the building for delivery to the analog signal delivering device.

12. An outstation control device as claimed in Claim 11 in which the microprocessor of the central processing unit comprises means to compute the temperature gain constant and temperature loss constant of the building under the control of the programme in the read only memory in the memory and clock card.

13. An outstation control device as claimed in Claim 12 in which the microprocessor of the central processing unit comprises means to compute the optimum start and stop times of the apparatus for varying the temperature of the building in response to the monitored temperatures and computed building constants under the programme in the read only memory of the memory and clock card.

14. An outstation control device as claimed in any preceding claim in which the analog signal receiving device receives signals from temperature sensors mounted inside and outside the building.

15. An outstation control device substantially as described herein with reference to and as illustrated in the accompanying drawings.

16. - Control apparatus for controlling a parameter at a number of locations in a building or compound, the control apparatus comprising a plurality of outstation control devices as claimed in any of Claims 1 to 15, one for each location, for controlling apparatus for varying the parameter of the location, the outstation control devices being connected in a network, and a central computer in the network communicating with the outstation control devices.

17. Control apparatus as claimed in Claim 16 in which each outstation control device comprises a serial data port for communicating with the other outstation control devices in the network, and a serial data port for communicating with the central computer.

18. Control apparatus as claimed in Claim 16 or 17 in which only one of the outstation control devices communicates directly with the central computer.

19. Control apparatus substantially as described herein with reference to and as illustrated in the accompanying drawings.

20. A method for controlling the temperature of a location in a building using an outstation control device as claimed in any of Claims 1 to 15 in which the method comprises the steps of monitoring the temperature inside and outside the building, computing the temperature gain constant and temperature loss constant of the building from the monitored data, computing the optimum start and stop times of apparatus for varying the temperature of the building in response to the monitored temperatures and computed constants and selecting a set of output signals from the loo up table in the memory and clock card corresponding to the computed temperature values, and delivering the set of signals to the apparatus for controlling the temperature of the building through the analog signal delivering device.

21. A method as claimed in Claim 20 in which the monitored temperatures are inputted to the device through the analog signal receiving device.

22. A method substantially as described herein with reference to and as illustrated in the accompanying drawings.