GB2195041A - Multi-sensor monitoring system - Google Patents

Abstract

A multi-sensor monitoring system comprises a plurality of sensor modules (4) for attachment to condition sensors (5-8) for generating condition signals on data buses (3). Each row of sensor modules (4) in Fig. 1 shares a respective data bus (3) to a respective digital data input port (2) of a programmable controller (1). Using one or more addressing ports (13), the controller (1) addresses the modules repeatedly, a column of modules being addressed simultaneously. When addressed, a module supplies over its data bus (3), one condition signal from each of its sensors (5-8). Each sensor has four condition lines (alarm, inhibit, fault, spare) and which is selected is determined by a control output port (16) of the controller (1). The controller (1) also has an autotest output port (17). <IMAGE>

Description

SPECIFICATION Multi-sensor monitoring system The invention relates to a -multi-sensor monitoring system.

Multi-sensor monitoring systems are used in a wide variety of fields particularly for process monitoring so as to control different stages in a process according to sensed process conditions and as safety systems where for example the existence of fire or gas is monitored.

One example of an application for such multi-sensor monitoring systems is for monitoring the existence of hazardous conditions for example on an off-shore platform. In this situation, a very large number of condition sensors such as heat, pressure, and process condition sensors are provided. Such a system must be highly reliable so as to prevent false alarms resulting in a partial or global shut down of the operation on the platform but to provide an accurate indication of a hazardous condition as soon as it arises. To achieve this, each condition sensor or addressable sensor is linked to a sensor module which is capable of sensing when the condition sensor itself is faulty.In addition, the output signals from the condition sensors are fed to a microprocessor or logic circuitry so that a fault condition is only indicated when a particular combination of output signals from the condition sensors is detected. To achieve this reliability, very complex monitoring systems have been developed for connection to several hundred condition sensors. In order to monitor the output signals from the condition sensors, the sensor modules to which the condition sensors are coupled are themselves grouped into sets, the sets being linked to scanner/multiplexer modules which rapidly scan the sensor modules in each set and pass the sensor address and the monitored data jn series to the microprocessor.The use of scanner/multiplexer modules has been necessary due to the relatively slow speed at which conventional microprocessors can receive the data on their serial input links. This, however, limited the amount of information available from the sensor modules since to speed up the rate at which data is suppiied to the microprocessor, the scanner modules only passed on change of state data ie. they were event driven.

In addition, the cost of these known systems is very high since with safety monitoring systems, in order to increase reliability it is common to duplicate or triplicate the system to provide redundancy.

In accordance with the present invention, a multi-sensor monitoring system comprises a plurality of sensor modules for attachment to condition sensors and for generating condition signals on respective data channels related to the conditions sensed by the sensors; and a processor having a plurality of data input ports, each data input port being connected with the data channels from a respective set of sensor modules, one or more addressing ports connected to address input ports of the modules, whereby the processor is adapted to scan the modules repeatedly such that each module in a set can be addressed to supply data along its data channel to the respective data input port, and logic means responsive to data received at the input ports to generate corresponding output signals.

This monitoring system has a considerably reduced cost compared with conventional systems, particularly when the system has to be duplicated or triplicated, by connecting the sensor modules directly with the data input ports of the processor. The scanning function is thus achieved by the processor itself and the intermediate scanner modules previously required are completely dispensed with. The processor may conveniently be provided by a conventional programmable controller which has the facility of very rapidly scanning its digital input ports. Thus, the data channels may be connected with the digital input ports of the programmable controller and not, as hitherto, to the serial input port.

The elimination of the scanner/muitiplexer modules considerably reduces the cost of the system while the ability to use conventional programmable controllers allows multi-function monitoring systems to be developed very easily since the programmable nature of the controller enables the programmed logic easily to be changed depending upon the application (safety monitoring, process control etc) with which the monitoring system is used. In addition the omission of the scanner/multiplexer modules removes the additional communication protocols previously required.

Preferably, the data channels of each set of sensor modules are connected to a common data bus, each data bus being coupled with a respective data input port of the processor.

This reduces the complexity of the system still further.

It is particularly advantageous if the system further comprises a plurality of address buses, one module from each set being connected to a respective common address bus, the address buses being connected with the same or respective addressing ports, whereby each module connected to the same address bus can be addressed by a single addressing signal to pass data along the data channels to the processor.

By linking the modules of the sets in this way, data from one module from each set can be received simultaneously by the processor resulting in a very rapid scanning operation.

Conveniently, a single address port is provided to which all the common address buses are connected.

Although each sensor module may be con nected to a condition sensor which generates its relevant type of information (eg. alarm/fault signals), one or more of the sensor modules may be adapted to receive more than one signal type from each condition sensor to which it is connected, the processor further comprising a - control port connected with control input ports of the modules, whereby signals issued by the processor from the control port determine which condition sensor data is to be accessed.

As with the address buses, the system may comprise a plurality of control buses connected to the same or respective control ports of the processor, one module from each set being connected to a respective common control bus.

The output signals generated by the logic means may be used in a variety of convention ways. For example, to operate indication means such as a display or recording device or directly or indirectly to control part of a process being monitored. Typically, the processor will be duplicated or triplicated with the output signals being fed to decision logic for-issuing a final control signal based on two out of three logic or the like.

An example of a multi-sensor monitoring system according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a block diagram of part of the system; and, Figure 2 is a block diagram of one of the sensor modules shown in Figure 1.

The monitoring system to be described is a safety monitoring system for use, for example, on an offshore drilling platform. Part of the system is shown in Figure 1 and includes a central processor 1 which may comprise a conventional programmable controller such as a General Electric Series 6 programmable controller.

The programmable controller 1 has a number of digital I/O ports 2, two of which are shown in Figure 1. Each of these ports 2 is connected to a data bus 3 (typically four lines). Each data bus 3 is coupled in parallel with a set of typically 14 sensor modules 4.

Each of the sensor modules 4 may be of a conventional type such as our G120 modules.

In practice, each of the modules 4 of a set will be mounted in a common rack (not shown). Although only two sets of modules are shown in Figure 1, a conventional programmable controller could support up to 250 racks each containing 3500 modules giving a typical input capacity of 14,000 switched inputs or 7000 gas inputs. The sensor modules shown in Figure 1 are all four channel switched modules which can be coupled with fire sensors, switches or any switch device complying with the input current requirements.

One or more of these modules could be replaced by a two channel gas module linked with a gas sensor. Other modules can be used for interfacing up to 32 input channels.

As can be seen in Figure 1, each sensor module 4 is coupled by respective four line data channels with four condition sensors 5-8, only four of which are shown in Figure 1.

Each sensor module 4 has an address port 9 with the address ports of corresponding modules 4 in different sets being connected to common address buses, three of which 1012 are illustrated in Figure 1. Each of the address buses 10-12 is connected to an address port 13 of the programmable controller 1.

Each sensor module 4 also has a control port 19 with the control ports 19 of corresponding sensor modules 4 in each set being coupled with common control buses 15. Each control bus 15 is coupled with a control port 16 of the programmable controller 1.

The programmable controller 1 also has an autotest port 17 connected to a typically 14 line bus 18 each line of which is connected in parallel to an autotest port 14 of corresponding sensor modules 4 of each set of modules.

The construction of each module 4 is shown in more detail in Figure 2. The module includes a data selector 20 for each sensor input each of which is coupled by typically four data lines 21-24 to a respective condition sensor such as a temperature sensor, pressure sensor, or switch position sensor. A control bus buffer 25 is connected to the control input port 19 of the module while an address bus buffer 26 is connected to the address input port 9 of the module. The control bus buffer has two output ports CO, C1 each of which is connected in parallel with the data selectors 20. Two further output ports of the control bus buffer 25 are connected to address decode logic 27 via lines 28, 29. The address bus buffer 26 is connected by typically four lines to address ports AO-A3 of the address decode logic 27.An enable output port of the address decode logic 27 is coupled by a line 30 to an input port of an output driver circuit 31. The output driver circuit 31 is coupled by typically four lines 32 with the data bus 3.

Each condition sensor provides a digital output signal on the lines 21 which in one state indicates either an alarm condition and in the other state indicates a normal condition. On the lines 22 each condition sensor generates a signal indicating whether it has been inhibited or not while the lines 23 a signal is generated indicating whether or not the condition sensor has developed a fault. Each line 24 is a spare line. (For an analogue sensor the analogue value is also transmitted on the data lines in binary code).

In use, the programmable controller issues an address from its address port 13 which is applied to each of the sensor modules 4. Each sensor module 4 linked by a common address bus 10 has the same address. The address generated from the address port 13 is fed from the address bus 10 to the address bus buffer 26 of each sensor module and from there to the address decode logic 27 where it is compared with the module address. If the addresses are the same, the address decode logic 27 issues an enable signal on the line 30 to enable the output drive circuit 31. At the same time, a control signal is generated by the programmable controller 1 from its control port 16 which is received by the sensor modules 4. This signal of typically four bits is fed to each control bus buffer 25 and typically the first two bits are output on lines CO C1 to each data selector 20.These bits determine which of the four lines connected to each data selector 20 is passed to the output driver circuit 31. For example, if both bits are zero then the signals on the lines 21 will each be passed to the output driver circuit 31.

The third digit of the control signal typically constitutes an "address valid" bit while the fourth bit is a read/write digit controlling whether the module is being addressed (output module) or whether the sensor module address is to be set on set address ports BO B3 (input module). The selected data is passed from each data selector 20 via the output driver circuit 31 to respective lines of the data bus 3 and from there to the respective data input port 2. It will be appreciated that data will be received simultaneously by each data input port from the sensor modules 4 which have the same addresses. The programmable controller is programmed in a conventional manner to apply a decision algorithm to the incoming data to decide whether an alarm condition exists and to issue an appropriate output signal from an output port 33.

In practice, although not shown, the system of Figure 1 will be duplicated with two separate processors being connected to a simple x input module with dual addressing capability and similarly to simplex output modules with dual addressing capability further decision logic which issues In practice, several different output ports may be provided for indicating alarm conditions sensed by different groups of the condition sensors so that different actions can be taken. The output signals may simply cause a display of the alarm condition to be activated or cause part of a process to be shut down or the like.

In a typical scanning operation, the program mable controller 1 will generate address and control signals so that the signals on the lines 21-24 are accessed in the order: all modules 21, all modules 22, all modules 21, all modules 23, all modules 21, all modules 24. In this way, the indication of an alarm condition on the line 21 will be detected very quickly.

In addition, at the end of each full scan, the programmable controller 1 will issue a reserved address which is different from any of the module addresses and will then check that no signals are received on the data buses.

This provides an integrity check.

Periodically, the programmable controller 1 will issue an auto-test signal from the autotest port 17 which forces all the data outputs that are not inhibited to the alarm state. The auto-test signal will be applied in turn to each group of the modules 4 connected in parallel to the same line of the auto-test bus and the programmable controller then checks that alarm condition signals are received at each input port 2.

Claims (9)

1. A multi-sensor monitoring system comprising a plurality of sensor modules for attachment to condition sensors and for generating condition signals on respective data channels related to the conditions sensed by the sensors; and a processor having a plurality of data input ports, each data input port being connected with the data channels from a respective set of sensor modules, one or more addressing ports connected to address input ports of the modules, whereby the processor is adapted to scan the modules repeatedly such that each module in a set can be addressed to supply data along its data channel to the respective data input port, and logic means responsive to data received at the input ports to generate corresponding output signals.

2. A system according to claim 1, wherein the data channels of each set of sensor modules are connected to a common data bus, each data bus being coupled with a respective data input port of the processor.

3. A system according to claim 1 or claim 2, further comprising a plurality of address buses, one module from each set being connected to a respective common address bus, the address buses being connected with the same or respective addressing ports, whereby each module connected to the same address bus can be addressed by a single addressing signal to pass data along the data channels to the processor.

4. A system according to any of the preceding claims, wherein at least one of the sensor modules is adapted to receive more than one signal type from the or each condition sensor to which it is connected, the processor further comprising a control port connected with control input ports of the modules, whereby signals issued by the processor from the control port determine which condition sensor data is to be accessed.

5. A system according to claim 4, further comprising a plurality of control buses connected to the same or respective control ports of the processor, one module from each set being connected to a respective common con troi bus.

6. A system according to any of the pre ceding claims, wherein the processor comprises a programmable controller, the data input ports comprising digital I/O ports of the controller.

7. A system according to any of the preceding claims, further comprising indicating means connected to the processor and responsive to the or each output signal to provide an indication of the conditions sensed.

8. A multi-sensor monitoring system substantially as hereinbefore described with reference to the accompanying drawings.

9. A safety monitoring system according to any of the preceding claims.