CONTROL SYSTEM

Abstract: A communication system in a domestic heating system allows multiple independent parameters to be ready by the controller (1) via a single sensor input channel of two wires (2 or 6). Accordingly, the A/D conversion operation is effected at the controller, ensuring more accurate conversion than if done in the remote units (3, 7); moreover, the cost of each remote unit is thereby reduced. Furthermore, once the "channel" between the controller and a given remote unit is selected, it can be treated like any other sensor channel by the controller.

Description: CONTROL SYSTEM The present invention relates to a communication system between a central controller and remote units. In one form of communication system, digital signal are used to transfer the requisite information between the central controller and its remote units. However, as the remote units typically have analogue sensors, the remote units need to incorporate A/D converters which for cost reasons tend to be simple and of limited accuracy. In one type of system involving the transmission of analogue signals, the remote unit sends to the controller an analogue signal whose value is a combination of an override switch status and the set-point value. In another type of system, there is sent a single value signal being the difference between the sensor and set-point values in combination with the override status. The two latter types of system suffer from the disadvantages of limited range (and signal-to-noise ratio) of each signal as the available range is divided up by the number of switch positions (plus guardbands). The present invention provides a heating and /or cooling control system comprising a central controller, a two-wire link for connecting the controller and a remote unit to send information in analogue format to the controller, the controller characterised by means to instruct the remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data, the instruction means comprising means to transmit a digital signal of a variety of number and/or duration of pulses, the remote unit comprising means to switch between a plurality of circuit branches dependent on the digital signals received from the instruction means. In this way, the remote unit can send separately a plurality of types of information (e.g. sensor information and set-point information), by providing separately readable channels while only requiring a simple 2- wire connection. The present invention also provides a method of operating a heating and /or cooling control system comprising a central controller, a two-wire link for connecting the controller and a remote unit to send information in analogue format to the controller, the method characterised by instructing the remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data, the instruction step comprising transmitting a digital signal of a variety of number and/or duration pulses, the remote unit switching between a plurality or circuit branches dependent on the digital signals received from the instruction step. Preferably the instruction means is able to send one pulse (to select sensor information), or two pulses (to select set-point information) or four pulses (to select override switch state information), and so the particular signal switches in the appropriate circuit elements in order to present to the controller the appropriate impedance or voltage value across the input of the remote unit. Accordingly, the A/D conversion operation is effected at the controller, ensuring more accurate conversion than if done in the remote units; moreover, the cost of each remote unit is thereby reduced. The invention also provides simple low cost digital channel selection hardware/ protocol, and automatic reset after a timeout period avoiding the need to reset the unit after a read. One preferred application provides a domestic heating control system comprising a boiler controllable by a central controller, a two-wire link for connecting the controller to a first remote unit in a first heating zone (e.g. being the living quarters), whereby the first remote unit sends information in analogue format to the controller, a second two-wire link for connecting the controller to a second remote unit in a second heating zone (e.g. being the bedrooms), whereby the second remote unit sends information in analogue format to the controller, means to instruct each remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data, the instruction means comprising means to transmit a digital signal of a variety of number and/or duration of pulses, each of the remote units comprising means to switch between a plurality of circuit branches dependent on the digital signals received from the instruction means. Thus the present invention also provides a method of operating a domestic heating control system comprising a boiler controllable by a central controller, a two-wire link for connecting the controller to a first remote unit in a first heating zone (e.g. being the living quarters), whereby the first remote unit sends information in analogue format to the controller, a second two-wire link for connecting the controller to a second remote unit in a second heating zone (e.g. being the bedrooms), whereby the second remote unit sends information in analogue format to the controller, the method comprising instructing the remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data by transmitting a digital signal of a variety of number and/or duration of pulses and then the appropriate remote unit switching between a plurality of circuit branches dependent on the digital signals received from the instruction means. In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the accompanying drawings in which: Figure 1 is a schematic diagram of a control system embodying the present invention; Figure 2 is a block diagram in greater detail of the system of Claim 1; Figures 3a and 3b are graphs of the waveforms of the systems of Figure 1; Figure 4 is a block diagram of a modification to the remote unit of Figure 2; and Figure 5 is a circuit diagram of the remote unit of Figure 4. Figure 1 shows a control system of the present invention incorporated in a domestic heating system and having a central controller 1 connected via two low-voltage wires 2 to a remote unit 3 located in heating zone 4 being the living quarters of a house. Upon request by controller 1, unit 3 sends information to it concerning sensor information, set-point information, or override switch state information, such information being used by controller 1 in operating boiler 5 of the heating system. Likewise, controller 1 is connected via two low-voltage wires 6 to a remote unit 7 located in heating zone 8 being the bedrooms in the house, with unit 7 sending equivalent information when so requested by controller 1. Controller 1 is also linked to a sensor 9 located outside the house to provide the controller with information on the exterior temperature; as sensor 9 provides only one type of information, it does not utilise the features of the invention. The central controller 1 provides DC power to the remote unit 3 for a period, then removes the power. Controller 1 then sends a number of voltage pulses to remote unit 3. On detection of each pulse, the remote unit switches the next circuit branch in sequence onto the 2-wire connection. Provided that the voltage resulting from switching in a branch does not cause the pulse detection threshold to be crossed, the selected branch will remain switched to the 2-wire connection until another pulse is sent by the instruction means. Remote unit 7 operates in the same manner. In the specific implementation shown in Figure 2, power scheduler 10 in the central controller 1 closes power switch 12 to switch Vdc onto the low voltage wires 2 at time To (see Figure 3a) for a period, thereby to provide remote unit 3 with sufficient charge to power a supply 13 in order to sustain the remote unit circuitry during the subsequent unpowered period. Power scheduler 10 then opens power switch 12 at time Tl, disconnecting power from the line 2. The voltage across wires 2 is then pulled up through pull-up resistor 14 to Vdc. Microprocessor- based instruction means 11 then closes a signalling switch 15 (also at time Tl) shorting the two-wire connection 2 so that line voltage becomes zero. At time T2, signalling switch opens, this forming a pulse which crosses V threshold (Figure 3a) in branch selector 16 which then closes switch 17 connecting branch 18 across the line 2. The resultant voltage at time T2 is then proportional to the resistance value of branch 17. After a settling time, measurement circuit 19 in the controller 1 reads the voltage across line 2 at time Tr. Figure 3b shows the situation in which two pulses are transmitted by the controller, in order to select the set-point information; thus at time T3, instruction means 11 again closes signalling switch 15, making line voltage zero and then opening switch 15 at time T4. Branch selector 16 detects V threshold being crossed and selects the next branch in sequence by opening switch 17 and closing switch 20 connecting branch 21 across the line 2. The resultant line voltage is then proportional to the resistance value of branch 21. Measurement circuit 19 then reads the line voltage after a settling period at time Tr. The system operates in similar fashion when controller 1 transmits four pulses in order to select the override switch state information. By knowing the number of pulses sent out, the controller is aware of the type of information represented by the response; in addition, controller 1 does a range check to ensure that the value of the response is consistent with the type of information it represents. If the controller 1 incorporates a shift register rather than a binary counter, then the number of pulses used for selection would be one, two and three. After a timeout period (i.e. at time Tt) the branch selector 16 resets to its initial state with no branch selector switches 17, 20 closed and the line 2 is pulled up to Vdc through pull-up resistor 14. At some time after Tt, power scheduler 11 closes switch 12 again starting the cycle again at time TO. Figure 4 shows a modification to the remote unit 2 of Figure 2 whereby the branch selector 16 had been extended to provide an auxiliary control function. If more pulses are sent than that required to select the last branch, this condition can be used to provide one or more control signals to enhance the remote unit functionality. Specifically, in the system described above with three branches requiring 1, 2 and 4 pulses respectively to select them, if eight pulses are sent the branch selector 16 generates a signal which is used to reset a latch 22. The latch 22 (Party mode request in this case) is set manually by a momentary switch 23 and reset by the instruction means 11 in the central controller 1 via the branch selector 16 after a predetermined period of time dependent on the mode of operation of the central controller 1. This has the advantage that by simply adding one or more stages to the basic branch selection mechanism, simple control can be achieved at the remote unit and basic two way communication can be implemented in conjunction with the analogue channel from the remote unit. This allows the relatively complex function with behaviour variable dependent on the central controller state to be made available at the remote unit with minimal overhead in the remote unit. In this case, the Party mode request is read as an analogue value (override branch resistance change) and the latched state is reset digitally. In an implementation of the system described, the three branch selection signals use three stages of a 4-stage binary counter integrated circuit and the Party mode reset function makes use of the fourth stage. Figure 5 shows in greater detail the modified system of Figure 4. The remote unit function provides space sensor information, parallel shift information, and override switch information through a single sensor channel to an OTC controller via a low voltage two-wire link. This link provides power and selection signals to the unit and is used to present the selected information in terms of a resistance to the controller. The resistance is then converted using a pull-up resistor in the controller into a voltage, in the same way as the other sensors attached to the controller. Power is supplied to the remote unit from the 5V supply in the controller to charge up its reservoir capacitor Cl then the power is removed to allow signalling and resistance measurement to take place. Diode CR1 prevents discharge of Cl to the line when the power is removed and isolates the parallel impedance of the rest of the circuit from the resistance being measured. The voltage at Cl is approximately 4.1V due to voltage drops in the controller power switching transistor and blocking diode CR1. After the initial charge-up of the capacitor, only a short recharge period (< 10ms) is required, the unpowered period being about 100 ms. The controller makes a measurement once every few seconds, leaving power on the unit the rest of the time; the measurement rate can be increased for test/ calibration purposes. CR2 protects the comparator input from a negative voltage if the unit is mis-wired as the power supply in the controller will see a short circuit and go into current limit so that the controller does not function until the unit is correctly wired. When the power is removed, the remote unit is supplied from the 5V through a pullup resistor to allow signalling to take place. After the power is removed, the line remains high due to the pull-up then the controller transmits a number of low 75us wide pulses to the unit by switching a transistor across the line. The time between pulses is also 75us. The first low pulse is detected by comparator U2A at a threshold of 0.55V approx. This results in buffer U2B output being held low for long enough to discharge reset timeout capacitor C3 via diode CR3. This in turn through comparator U2C and Q7, removes the reset on U1A within about 25us from the falling edge of the pulse. The active pullup using Q7 makes the rising edge of the clear signal fast enough to avoid spurious output pulses from U1A during the transition. A threshold of approx. 3.2V is used on comparators U2B,C,D. At the end of the pulse, the line going high results in the clock to the counter U1A going low, incrementing the counter (ie. to a count of 1). The count of 1 switches on Q l presenting the Space Sensor arm resistance across the line. If a second pulse is sent, Q4 switches on presenting the Parallel Shift arm resistance across the line. If a third and fourth pulse are sent, Q6 switches the Override Switch arm resistance across the line. If 8 pulses are sent a signal is generated which, through CR4, clears the 3-hour Extension or "Party Mode" latch (counter U1B). This function is described in a subsequent section. None of the resistance arms are presented to the line when this signal is active. When the line goes high after the selection pulses, the U2B output goes high allowing C3 to charge up again via R8. After a period of about 150ms it charges up sufficiently to make U2C output go low, making the Q7 collector go high, holding the counter reset in preparation for the next measurement cycle. The additional transistors in the selection circuit (Q2,3,5) prevent intermediate U1A counts (3,5,6,7) from causing more than one arm to be selected. This prevents a low parallel resistance which would pull the line down and present spurious clock edges to the counter. In all cases the lowest order arm in a combination will be selected. For a resistance measurement, a voltage is produced on the bus by the 5 volt controller supply and the voltage divider comprising the controller pullup resistor and the resistance selected in the unit. This is then measured by the A/D circuit in the controller and converted by the software into temperature and override information. The Space Sensor Arm comprises NTC thermistor RT1 in series with calibration pot R9. The Parallel Shift Arm comprises the Parallel shift pot R21 in series with offset resistor R20 and calibration pot R19. The Override Switch Arm resistance comprises one of three values corresponding to the DAY, AUTO and NIGHT (or Comfort Auto and Setback) positions of SW1 , in series with offset resistor R28. R28 can be shorted out by Q8 to signal a Party Mode request (as described in the next section), so each mode will have two corresponding values of resistance. In the Party Mode, a pulse produced by pressing momentary switch SW2 toggles counter U 1B. U2D, C5, R24 and R26 debounce the switch, providing a clean pulse to clock the counter. The LSB of the counter drives LED 1 to indicate that a 3-hour extension to comfort mode has been requested. The counter effectively latches this request. Pressing SW2 again causes the request. Pressing SW2 again causes the request to be cancelled, turning off LED 1. The LED drive signal also turns on FET Q8 shorting out R28, resulting in a reduction in the Override Switch arm resistance. This change is recognised by the controller. As indicated in the Resistance Selection section, the controller sends an 8-pulse sequence to clear the Party status flag, turning LED 1 off. When the Override Switch is in the DAY position, R32 holds U12B clear high, and pressing SW2 does not cause LED 1 or Q8 to go on. R34 and R35 are provision for future version to allow SW2 to be used in a different way. C7 is necessary to prevent reset of U1B by fast transients induced on the line. Cl also protects the circuit from the effect of transients.

Claims: CLAIMS 1. A heating and /or cooling control system comprising a central controller, a two-wire link for connecting the controller and a remote unit to send information in analogue format to the controller, the controller characterised by means to instruct the remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data, the instruction means comprising means to transmit a digital signal of a variety of number and/or duration of pulses, the remote unit comprising means to switch between a plurality of circuit branches dependent on the digital signals received from the instruction means. 2. A system according to Claim 1 , characterised by a plurality of remote units, each having a separate two-wire link to the controller. 3. A system according to Claim 1 or 2 characterised in that the instruction means is able to send any one of a plurality of pulsed signals so the particular signal switches in the appropriate circuit elements of the remote unit in order to present the appropriate impedance or voltage value across the two wires from the remote unit to the controller. 4. A system according to any preceding Claim characterised in that the instruction means is able to select between any one or more of the following types of data: sensor information, set-point information, override switch state information. u 5. A system according to any preceding Claim, characterised in that the instruction outputs one, two or four pulses to select which type of data to be transmitted by the remote unit. 6. A domestic heating control system comprising a boiler controllable by a central controller, a two-wire link for connecting the controller to a first remote unit in a first heating zone (e.g. being the living quarters), whereby the first remote unit sends information in analogue format to the controller, a second two-wire link for connecting the controller to a second remote unit in a second heating zone (e.g. being the bedrooms), whereby the second remote unit sends information in analogue format to the controller, means to instruct each remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data, the instruction means comprising means to transmit a digital signal of a variety of number and/or duration of pulses, each of the remote units comprising means to switch between a plurality of circuit branches dependent on the digital signals received from the instruction means. 7. A method of operating a heating and /or cooling control system comprising a central controller, a two-wire link for connecting the controller and a remote unit to send information in analogue format to the controller, the method characterised by instructing the remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data, the instruction step comprising transmitting a digital signal of a variety of number and/or duration pulses, the remote unit switching between a plurality or circuit branches dependent on the digital signals received from the instruction step. 8. A method according to Claim 7 characterised by instructing a plurality of remote units, each having a separate two-wire link to the controller. 9. A method according to Claim 7 or 8 characterised in that the instruction step comprises sending any one of a plurality of pulsed signals so the particular signal switches in the appropriate circuit elements of the remote unit in order to present the appropriate impedance or voltage value across the two wires from the remote unit to the controller. 10. A method according to any of Claim 7 to 9 characterised in that the instruction step comprises selecting between any one or more of the following types of data: sensor information, set-point information, override switch state information. 11. A method according to any of Claims 7 to 10 characterised in that the instruction step comprises outputting one, two or four pulses to select which type of data to be transmitted by the remote unit. 12. A method of operating a domestic heating control system comprising a boiler controllable by a central controller, a two-wire link for connecting the controller to a first remote unit in a first heating zone (e.g. being the living quarters), whereby the first remote unit sends information in analogue format to the controller, a second two-wire link for connecting the controller to a second remote unit in a second heating zone (e.g. being the bedrooms), whereby the second remote unit sends information in analogue format to the controller, the method comprising instructing the remote unit to selectively transmit an analogue signal representing a specified one of a plurality of different types of data by transmitting a digital signal of a variety of number and /or duration of pulses and then the appropriate remote unit switching between a plurality of circuit branches dependent on the digital signals received from the instruction means.

Inventors: MACKIE ALASTAIR DAVID, MACKIE, ALASTAIR, DAVID
Applicants: HONEYWELL CONTROL SYST, MACKIE ALASTAIR DAVID, HONEYWELL CONTROL SYSTEMS LIMITED, MACKIE, ALASTAIR, DAVID
Application year: 1995
Main classification: G05D23
IPC codes: G05D23, H04Q9