Intrinsically safe portable programmer for enclosed electronic process control equipment

FIELD OF THE INVENTION

The present invention relates to enclosed electronic process control equipment, and more particularly to an intrinsically safe portable programmer for communicating with the electronic process control equipment without electrical connection between the two.

BACKGROUND OF THE INVENTION

Level measurement systems are one type of electronic process control device. Level measurement systems, also known as time of flight ranging systems, determine the distance to a reflector or reflective surface (e.g. the level of a liquid held in a storage tank) by measuring how long after transmission of a burst of energy pulses, the echo is received. Such systems typically utilize ultrasonic pulses, pulse radar signals, or microwave energy signals. Level measurement systems find widespread application in many different types of process control applications in a wide variety of diverse applications, such as the petroleum industry and the food industry.

Industrial process control applications in hazardous environments, such as the petroleum industry, often require the electronic process control equipment to be installed as enclosed devices for safety reasons. Once installed, the enclosed devices are inaccessible even for purposes of routine maintenance, programming and calibration. To access the device, the industrial process or processes operating in the work space must be disabled and the area deemed declassified, and only then can the electronic process control equipment be opened for maintenance or reprogramming.

The programming, calibration, and/or configuration of such electronic process control equipment is often performed using an on-board keypad or control panel. The keypad is accessed by opening the device after the industrial process and work space have been disabled and declassified. It will be appreciated that while the keypad is a necessary component to provide the capability for configuring, calibrating, and re-programming the device, the keypad is a component which does add to the cost of the device. In the case of enclosed electronic process control devices in hazardous environments, the switches or pushbuttons for the keypad must be explosion proof which adds further to the cost of the electronic process control device. Furthermore, the declassifying operation for a hazardous area is both time consuming and costly.

Accordingly, there remains a need for an apparatus which would facilitate the programming of enclosed electronic process control devices in a hazardous area.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an intrinsically safe portable or handheld programming device suitable for enclosed electronic process control equipment, such as level measurement devices.

In a first aspect, the present invention provides an intrinsically safe portable device for configuring the operation of electronic process control equipment, the electronic process control equipment includes a wireless communication receiver, the portable device comprises: (a) an enclosure; (b) an electronic circuit mounted in the enclosure; (c) a keypad coupled to the electronic circuit; (d) a wireless transmitter responsive to the electronic circuit and operative to transmit control signals to the wireless communication receiver on the electronic process control equipment for controlling the operation of the electronic process control equipment; (e) the electronic circuit includes a low voltage power supply and a low power microcontroller for operating at a low voltage level to eliminate the incidence of sparking.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which show, by way of example, a preferred embodiment of the present invention, and in which:

FIG. 1

is a block diagram of a level measurement system and an intrinsically safe handheld programmer according to the present invention;

FIG. 2

is a diagrammatic exploded view of the intrinsically safe handheld programmer according to the present invention;

FIG. 3

is a schematic diagram showing an implementation of the electronic circuit for the intrinsically safe handheld programmer of FIG.

2

.

DETAILED DESCRIPTION THE PREFERRED EMBODIMENT

Reference is first made to

FIG. 1

which shows an intrinsically safe portable or handheld programmer

100

according to the present invention in conjunction with a level measurement instrument

10

in a typical hazardous industrial application. While the intrinsically safe handheld programmer

100

is described in the context of a level measurement instrument

100

, it is to be appreciated that the handheld programmer

100

has wider applicability to other types of electronic process control equipment.

With reference to

FIG. 1

, the level measurement instrument

10

is installed on a storage tank

12

and determines the distance to a reflector or reflective surface, i.e. the level of a liquid

14

held in the storage tank

12

, by measuring how long after transmission of a burst of energy pulses, the echo is received. Known level measurement systems

10

utilize ultrasonic pulses, pulse radar signals, or microwave energy signals.

The level measurement instrument

10

comprises a transducer

16

(e.g. an ultrasonic transmitter/receiver or a microwave waveguide ), a microcontroller unit (not shown), and an analog-to-digital converter (not shown). In some configurations, the level measurement instrument

10

is remotely coupled via an analog or digital communication interface (not shown). The transducer

16

is coupled to the microcontroller unit through a transmitter. The microcontroller unit uses the transmitter to excite the transducer

16

to emit energy waves, i.e. ultrasonic or microwave pulses. The reflected or echo pulses are received by the transducer

16

and converted into an electrical signal in a receiver.

The level measurement instrument

10

is installed in the container

12

, for example a tank, containing a material, such as the liquid

14

, with a level determined by the top surface of the liquid

14

. The top surface of the liquid

14

provides a reflective surface or reflector, indicated by reference

18

, which reflects the pulse (e.g. ultrasonic or microwave) generated from the emitter on the transducer

16

. The reflected pulse is coupled by the transducer

16

and converted by the receiver into an electrical signal which takes the form of a receive echo pulse waveform. The received echo pulse is sampled and digitized by an A/D converter (not shown) for further processing by the microcontroller unit. The microcontroller unit executes an algorithm which identifies and verifies the echo pulse and calculates the range of the reflective surface

18

, i.e. the time it takes for the reflected pulse, i.e. echo pulse, to travel from the reflective surface

18

to the receiver at the transducer

16

. From this calculation, the distance to the surface of the liquid

14

and thereby the level of the liquid is determined. The microcontroller also controls the transmission of data and control signals through the communication interface if one is installed. The microcontroller is suitably programmed to perform these operations as will be within the understanding of those skilled in the art. The detailed operation of level measurement systems

10

, or other types of electronic process control equipment, will be apparent to those skilled in the art and as such does not form part of the invention.

In accordance with the present invention, the intrinsically safe portable programmer

100

communicates with the level measurement device

10

through a wireless communication channel or link denoted by reference

101

. The wireless communication link

101

may comprise infrared, radio or other suitable wireless signaling. In the following description, the portable programmer

100

is described with reference to an infrared communication link. As shown in

FIG. 1

, the level measurement device

10

includes a wireless communication interface denoted by reference

20

. The wireless communication interface

20

comprises a receiver, and may also include a transmitter if two-way communication between the level measurement device

10

and the portable programmer

100

is desired. Similarly, the intrinsically safe portable programmer

100

includes a wireless communication interface

102

comprising a transmitter

230

(FIG.

3

). The wireless communication interface

102

may also include a receiver if two-way communication with the level measurement device

10

is desired.

Reference is next made to

FIG. 2

, which shows in greater detail the intrinsically safe portable or handheld programmer

100

according to the present invention. As shown in

FIG. 2

, the portable programmer

100

comprises an enclosure

110

, a keypad matrix

112

, a keypad overlay

114

, and an electronic circuit board

116

.

The enclosure

110

comprises a lid enclosure

111

and a base enclosure

113

. The lid

111

and base

112

enclosures are formed from general polymers polystyrene. The electronic circuit board

116

rests on standoff

118

in the base enclosure

113

. The keypad matrix

112

includes a pin connector

122

which is soldered directly to the electronic circuit board

116

. As shown in

FIG. 2

, the ribbon cable

122

fits through a slot

126

in the lid enclosure

111

. The electronic circuit board

116

also carries a battery

128

which provides the power supply for the electronic circuitry as will be described in more detail below. The other side of the electronic circuit board

116

carries the electronic circuitry as described in FIG.

3

. The standoff

118

includes a slot

120

for the infrared transmitter.

Reference is next made to

FIG. 3

, which shows an implementation of an electronic circuit

200

according to a preferred implementation for the handheld programmer

100

. The electronic circuit

200

comprises a microcontroller

210

, a power supply module

220

, and an infrared transmitter stage

230

. The microcontroller

210

is preferably implemented as a low power single chip microcontroller, such as the industry standard PIC type microcontrollers. As shown in

FIG. 3

, the microcontroller

210

has an output port

212

which drives the infrared transmitter stage

230

. The microcontroller

210

is also configured with an output port

214

and an input port

216

. The output port

214

comprises the scan lines for the keypad matrix

112

, and the input port

216

comprises the sense lines for the keypad matrix

112

. The scan lines

214

and the sense lines

216

are coupled to the electronic circuit board

116

via the pin connector

122

(FIG.

2

). In known manner, the microcontroller

210

is suitably programmed to perform a function for key pad scanning operation.

Referring still to

FIG. 3

, the power supply module

220

comprises the battery

128

(FIG.

2

), a fuse

222

, and a resistor

224

. The fuse

222

serves as a protective device, and the resistor

224

serves to limit the current drawn from the battery

128

. In order to facilitate meeting the design criteria for an intrinsically safe device, the power supply module

220

is implemented as a low voltage design, preferably in the range of 3 Volts. In the preferred embodiment, the battery

128

comprises a single cell lithium 3V battery. The circuit

200

is designed to consume no power when not activated, and this feature allows the circuit

200

to operate with the single battery

128

for several years. As will be described below, this is important because the circuitry is potted to meet intrinsically safe requirements, and as such the battery

128

cannot be replaced.

The infrared transmitter stage

230

provides the wireless communication interface

102

(

FIG. 1

) for transmitting control signals to program and adjust parameters in the electronic process control device

10

(FIG.

1

). As shown in Fig.

3

, the infrared transmitter stage

230

comprises a driver transistor

232

, and an infrared light emitting diode

234

(LED). Under the control of the firmware program in the microcontroller

210

, the drive transistor

232

is turned on causing the infrared LED

234

to emit infrared radiation which is detected by the infrared receiver

20

on the electronic process control equipment

10

(FIG.

1

).

The keypad

114

is configured to implement the control functions associated with the electronic process control equipment

10

and the microcontroller

210

is suitably programmed to scan the keypad

114

and implement these functions as will be within the understanding of one skilled in the art. For a level measurement device

10

, these functions include numerical operating parameter entry, mode selection, display output programming.

Reference is made back to

FIG. 2

, and as shown the lid enclosure

111

is secured to the base enclosure

113

via appropriate snap fasteners

130

and

132

which may be molded into the base enclosure

113

as shown in FIG.

2

. The keypad matrix

112

comprises a 4×5 key matrix. The keypad matrix

112

is coated with an adhesive coating on both top and bottom surfaces, for affixing the keypad matrix

112

to the top surface of the lid enclosure

111

and to the keypad overlay

114

, respectively.

To make the handheld programmer

100

intrinsically safe, the electronic circuit board

116

in the base enclosure

113

is encapsulated with a two-part non-conductive epoxy, such as Stycast 2075 epoxy. The polymers polystyrene for the enclosure

110

is preferably grade ESD Electrafil PS-31/EC, 40% Carbon Black with a maximum surface resistivity of 5,000E+03 Ohms.

Following the construction specifications and directions as described, a handheld programmer

100

in conformance with standard Group II Electrical Apparatus for Gas Atmospheres, per section EN 50014, is achievable.

Advantageously, the intrinsically safe handheld programmer

100

according to the present invention can eliminate the need for a keypad or control panel on the enclosed electronic process control device (e.g. level measurement device

10

in FIG.

1

). The keypad on the electronic process control device is replaced by an infrared receiver and a window over the receiver. Elimination of the keypad reduces the cost of the electronic process control device (for example the level measurement device

10

), and the in the case of an enclosed electronic process control device, elimination of a keypad with explosion proof keys or switches further reduces cost. Another cost saving benefit arising from replacing the keypad with an infrared receiver and transmissive window is that the housing for the electronic process control device can be reduced in size resulting in a further cost reduction.

According to another aspect, the hand held programmer

100

may be used with a family or entire product line of electronic process control devices in an industrial installation as further illustrated in FIG.

1

.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Certain adaptations and modifications of the invention will be obvious to those skilled in the art. Therefore, the presently discussed embodiments are considered to be illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.