GB2329983A - Portable device for monitoring output of measurement and control sensors - Google Patents

Abstract

The portable device comprises a microprocessor 20 for controlling the device, a memory 21 for storing data, and power supply battery 30. The device can be connected to and controlled by a computer to output data thereto and is also operable in stand alone mode, i.e. disconnected from the computer.Preferably the device is in the format of a PCMCIA card. The device can also be connected into a computer network.

Description

MONITORING DEVICE The present invention relates to a device for monitoring the output of one or more sensors.

Many types of specialized instruments used for measurement and control can be replaced by a personal computer (PC) fitted with an expansion card that allows the same tasks to be performed. A PC expansion card is a specially designed printed circuit board that can be inserted into one of the slots available on the motherboard of a desktop PC. The card generally adds new functions to the computer, in this case, the ability to monitor and control external digital or analog systems. A PC extended by such a card is more powerful and less expensive than a dedicated instrument and allows access to the vast amount of data analysis software readily available for the PC.

Accordingly, this approach to instrumentation is becoming increasingly popular. However, one disadvantage of an extended desktop PC is that, unlike a specialized instrument; it is not portable. In addition, notebook or portable PCs have no room for the kind of expansion card described above. Portable PCs are provided with smaller expansion interfaces into which credit-card sized PCMCIA (Personal Computer Memory Card International Association) cards can be inserted. However, the small size of a PCMCIA card severely limits the features it can add to a PC.

A further disadvantage of PC instrumentation when used for continuous monitoring is that the PC is permanently unavailable for other tasks and the system is then more expensive than the use of a standard specialized instrument.

Another trend is the installation of specialized networks to link instruments together so that data can be exchanged between them and analysed at a central point.

However, such networks tend to be very expensive.

It is therefore an object of the invention to alleviate at least some of the disadvantages of the prior art that have been described, and to simplify and reduce the cost of instrumentation used for measurement and control.

The present invention provides a portable device for monitoring the output of one or more sensors, the device comprising processing means for controlling the device, memory means for storing data and power supply means, wherein the device can be connected to a computer and operated under control of the computer to output data thereto and is also operable when disconnected from the computer.

In a preferred embodiment, the device is in the format of a PCMCIA card and can therefore be inserted into a portable PC. The processing means preferably comprises a microprocessor and the power supply means preferably comprises a battery which is used only when the device is disconnected or not directly connected to the PC (stand alone mode). The device can be left to continuously monitor sensors by itself and to store sensed data in the memory means, the accumulated data then being retrievable by connecting the device to a PC.

The device may include a serial link that can be used to control a modem and communicate an appropriate signal in the event that a warning condition is detected.

Advantageously, the device may be operable to convert a hand-held terminal (which preferably has a PCMCIA interface) to which it is connected into a multimeter. If the device has previously been programmed from a PC with a route, an operator inserting the device into a hand-held terminal can be prompted to take readings from different locations, such as various pieces of equipment on a site.

Preferably, the device, whilst working in stand alone mode can be connected into a computer network, one or more computers of which are operable to control the device.

Accordingly, the present invention also provides a computer network (such as an Ethernet network) comprising at least one device as defined above. The device may be operable to emulate a PC and to drive an inexpensive network card connected to an ethernet network at a convenient node.

In order to provide a distributed monitoring system, the network may comprise a plurality of the devices, for example hundreds of the devices under the control of one computer.

In a method of operation of such a network, a device according to the invention is connected to the network and broadcasts a packet of data informing all the computers on the network that the device has been connected. The device then awaits a controlling packet of data including a valid address, password and command.

In order that the invention may be more readily understood, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1 is a perspective view of a device according to an embodiment of the invention; Figure 2 schematically shows the arrangement of components in the device of Figure 1; and Figure 3 is a schematic diagram showing different uses of the device of Figure 1.

Figures 1 & 2 show a device 1 in the form of a Type 2 PCMCIA card - a type generally used for input/output purposes. The card 1, which is a data acquisition card, comprises a credit-card sized housing 2 containing a printed circuit board and a 68-pin PCMCIA connector 3. In this particular embodiment, the card is specially adapted for measuring parameters like pressure and vibration in rotating machinery. The card 1 is EMC compliant and draws a maximum of 120mA from the host PC.

As shown in Figure 2, the card has a 16 bit microprocessor 20 and 256 kB of RAM 21. Power to the microprocessor is controlled by a power control 22. Whilst there are some connections directly between the microprocessor 20 and the PCMCIA connector 3, the main route for data between the card and the host PC is via interface logic in the form of a field programmable gated array (FPGA) 23. The FPGA handles the protocol by which the card 1 and the host PC communicate and, in the absence of such an array, approximately twenty integrated circuits would be needed for this function. The small size of the FPGA therefore allows all the components of the card 1 to be contained in the credit-card sized housing 2.

A standard 32-way socket 24 is provided at the opposite end of the card 1 from the connector 3, for signal inputs and outputs. The microprocessor 20 is connected to the socket 24 via a serial interface 25, via an analog-todigital convertor (ADC) 26, a filter 27 and an amplifier 28, and finally via trigger circuitry 29.

The memory 21 is backed up by a battery 30 which has an expected lifetime of three years and can be recharged in situ after a low battery warning is received from the card by the host PC.

Analog and Digital IO The card has a range of analog and digital lines. In the simplest operating mode, signals on any of the 6 analog input lines can be sampled at regular intervals. The acquired data block is stored locally then transferred to the host PC for analysis.

The digital input and output lines are available for closed-loop control applications.

The more advanced card functions require trigger inputs to enable sampling to be synchronised to the movement of the machinery being monitored.

Analog Inputs ChO 5V, + 10V, 5V, 10V (fault protected to + 16.5V) Chl +5V, + 10V, 5V, lOV (fault protected to + 16.5V) Ch2 As ChO/l but with 1.25kHz 4th order continuous digitally selectable low-pass filter (anti-aliasing).

Ch3 As Ch2 but with a digitally selectable x 1, x 10, x 100 programmable gain amplifier in front of the filter.

Ch4 0-5V (clamped by a 5.5V Zener Diode) Ch5 0-5V (clamped by a 5.5V Zener Diode) Digital Input DI6 Digital input line DI7 Digital input line DI8 Digital input line In an advanced function, pulses at DI8 are counted using an internal 32bit timer and the DI6 line is used to determine whether the counter counts up or down. The maximum frequency is 2.5 MHz.

Digital I/O DIO1 Digital input/output line DI02 Digital input/output line DI03 Digital input/output line In an advanced function, DIO1 can be used to send an interrupt to the PC on a positive, negative or either edge.

Digital output ADC Logic signal which undergoes a positive transition when the ADC 26 acquires data in pulse generation mode.

This can be used to activate slave ADCs in other units for parallel multichannel data acquisition.

Triaqer TD Digital logic pulse, positive edge.

FD Digital logic pulse, positive edge.

TA Analog trigger. Pulses may vary in amplitude from +lOmV to +1or.

FA Analog trigger. Pulses may vary in amplitude from +lOmV to +10V.

Data Acquisition The card uses a 12-bit 100 ksps ADC. The local processor can monitor any selected trigger input and synchronise data sampling to a specified number of equally spaced points between each pair of consecutive trigger pulses. With rotating machinery, the trigger normally indicates 0 or top dead centre (or indeed an arbitrary angular position). The card is then able to sample at regular angular intervals regardless of variations in speed from cycle to cycle. Data sets from many cycles can be averaged together to remove noise. Typically, 3,600 points are captured over each cycle (0.10 separation) and averaged over 10,000 cycles.

The maximum sampling rate in this mode is 60 kHz. The number of points per cycle is limited to 10,000 and the number of cycles to average over cannot exceed 100,000.

Double buffering of data allows bad cycles to be identified and the data rejected. The user may specify the number of bad cycles after which the acquisition process should terminate.

A second trigger input can be used to accurately gauge the angular position within the cycle. This is important where engines are being monitored (the firing of the cylinders causes substantial variation in speed within a cycle). The trigger signal may be obtained from a sensor placed near a toothed flywheel (if one is present). As the teeth pass the sensor, pulses are generated and are used by the processor to refine its estimate of the angular position.

The card can also average data using a software trigger. No separate trigger is required - the signal itself contains the trigger. The start-of-cycle indicator is defined as the point when the signal-exceeds a certain pre-determined level. Sampling then proceeds as before.

Note that single point measurements of any channel and the ability to measure at regular intervals as with a standard ADC card are also available to the user.

Sensors The card is able to drive a variety of sensors needed to provide the trigger signals.

Low-cost passive inductive position sensors can be connected directly to TA and FA. These could be used to detect the passing teeth of a flywheel. Note that these signals can be sampled by the ADC 26 to assist the operator in setting the optimum position for the sensors.

Ferrous proximity sensors or optical senors can be connected to the TD or FD inputs. Pins 24 and 25 of the socket are +12V taken directly from the PC and may be used to drive these transducers so long as the current drawn from each pin is limited to 30 mA.

If NPN digital senors are used two 8.2kQ resistors are available at pins 29-30 and 31-32 for connection between the sensor output and +5V (pin 28) for TTL compatible signals.

An optical encoder can be connected directly (drawing its power from the +5V card supply) with the two signals connected to TD and FD.

+5V and +12V supplies are available to drive the signal sensors. The card cannot drive +24V constant current pressure or acceleration sensors. If these are to be used, a suitable coupler must be obtained from the manufacturer.

A kit comprising a card, sensors and an appropriately wired cable can be supplied for most applications.

Software The card can be loaded with its operating program by the host PC in less than one second. Generally speaking this is only done if the software has to be upgraded from disks supplied by the manufacturer. The card is initially pre-programmed, but a copy of the software is also supplied.

If the backup battery is not recharged when requested, the software has to be loaded each time the card is powered on until the backup battery is recharged.

A program, preferably compatible with Windows (Trade Mark) allowing the user to access all the card functions, gather and display data is also supplied. While this will be adequate for most users, it will not be suitable for specialised applications. Accordingly, a Dynamic Link Library (DLL) with all the card functions can also be supplied along with comprehensive documentation and examples showing how an existing application can directly use the PC card. It is relatively easy to modify programs written in C++, Visual BASIC or Delphi to include an ACQUIRE DATA option on the application menu.

Figure 3 shows different methods of using the card 1, which is connected to sensors 4 for monitoring a system 5.

The card can be connected to a notebook PC 6. However, card 1 is effectively a complete microcomputer and does not require a PC to operate. It may be used with a hand-held terminal 7 with PCMCIA capability, or used as a stand alone miniature data logger. A serial port is available to enable acquired data to be extracted, for example via a modem 8, when operating in stand alone mode. A bootstrap loader can be activated to load the operating program over the serial port if a PC with a PCMCIA slot is not available.

A very important application is continuous monitoring in which the card 1 is permanently attached to the machinery. With this card, continuous monitoring can be achieved without tying up a PC by simply providing the card with a +5V power supply.

Getting data back from the card in continuous monitoring mode is very easy - it connects into a standard PC network 9 where it emulates a PC. Card operations can be controlled from any PC on the network.

An additional low-cost network interface 10 provides power to the card and a choice of a TPI, Thin Ethernet or Thick Ethernet connection. The typical sequence is for the card 1 to be inserted into the Interface unit. Following power up an identifier packet is broadcast over the network to inform all PCs (such as 11) the unit is on-line. The card then awaits packets with a valid instruction, the correct card address and password. Up to 26 instructions may be queued. The requests are processed one at a time with the data corresponding to each request sent back to the source PC in one or more packets. Note that it does not matter whether the network operating system is WINDOWS 3.11, WINDOWS 95 or WINDOWS NT (all trade marks).

Claims (10)

1. A portable device for monitoring the output of one or more sensors, the device comprising processing means for controlling the device, memory means for storing data and power supply means, wherein the device can be connected to a computer and operated under control of the computer to output data thereto and is also operable when disconnected from the computer.

2. A device according to claim 1, in the format of a PCMCIA card which can be inserted into a portable PC.

3. A device according to claim 1 or 2, wherein the processing means comprises a microprocessor.

4. A device according to claim 1, 2 or 3, wherein the power supply means comprises a battery which is used only when the device is disconnected or not directly connected to the computer.

5. A device according to any preceding claim, which can be left to continuously monitor sensors by itself and to store sensed data in the memory means, the accumulated data then being retrievable by connecting the device to the computer.

6. A device according to any preceding claim, including a serial link that can be used to control a modem and communicate an appropriate signal in the event that a warning condition is detected.

7. A device according to any preceding claim, which can be connected to a hand-held terminal in order to convert the terminal to a multimeter.

8. A device according to any preceding claim, which can be connected into a computer network, one or more computers of which network are operable to control the device.

9. A device for monitoring the output of one or more sensors, substantially as described herein with reference to the accompanying drawings.

10. A computer network comprising at least one device according to any preceding claim.