EP0792501A1

EP0792501A1 - Device for adapting hart actuators or sensors to a local area network, and method for using same

Info

Publication number: EP0792501A1
Application number: EP95940321A
Authority: EP
Inventors: Guy Benoit
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1994-11-18
Filing date: 1995-11-16
Publication date: 1997-09-03
Anticipated expiration: 2015-11-16
Also published as: DE69508424D1; JPH10509261A; EP0792501B1; FR2727230B1; WO1996016384A1; FR2727230A1; DE69508424T2

Abstract

A device for adapting HART actuators or sensors to a local area network, including a first galvanic insulation stage (35), a filtering amplifier (36), a shaping discriminator (37), a modem (38) for restoring coded digital data, a programmed microcontroller (39) for translating messages into the local network language, an interface circuit (40) and a second galvanic insulation stage (41). A method for using said device is also disclosed.

Description

DEVICE FOR ADAPTING SENSORS OR ACTUATORS OF THE TYPE

"HART" WITH A LOCAL INDUSTRIAL NETWORK AND METHOD OF SETTING

IMPLEMENTATION OF THIS DEVICE

DESCRIPTION

Technical area

The present invention relates to a device for adapting sensors or actuators of the "HART" type (registered trademark) with an industrial locar network, for example of the "FIP" type or of the "PROFIBUS" type, and a method of setting up work of this device.

State of the art

For many years, the sensors used in automation have used a 4-20 mA output to transmit their measurement. The current of 4 mA corresponds to the minimum measured value and 20 mA to the maximum value. Sensors and actuators are now "intelligent". It is possible to communicate with them to implement advanced functions such as changing the range, unit, testing, calibration possibilities, etc. The output information is digitized, which implies a notion of coding. Unfortunately, there are many different encodings, which creates an incompatibility between them.

To connect the automation devices (sensors, actuators, programmable logic controllers, computers, etc.) today, a field network is preferably used, for example "HART 'from Rosemount, or" FIP ". HART 'is described in an article entitled "The HART® Communication Protocol" (published in bulletin F 2695, Rev 0-11 / 91, "The Smart Family", Rosemount). This protocol is also described in the article entitled "HART PROTOCOL" by Romilly Bowden (June 1991, available from Rosemount). A "HART" modem is described in an article entitled "HART 'MODEM, ultra low power modem chip" (NCR 20C12, NCR "handbook").

"HART '(Highway Addressable Remote Transducer) is the name Rosemount gives to its communication protocol for" smart "transmitters.

"HART" uses the BELL 202 communication standard which is based on frequency modulation signal transmission with 2 specific frequencies. The communication speed is 1200 baud.

The main characteristics of "HART 'are as follows: - It allows both analog and digital communication. Access to digital data can be done while using the analog signal for regulation or measurement.

- The same set of electronic cards makes it possible to establish a digital link with "2-wire" transmitters or total digital communication. Instructors can begin using "smart" transmitters with current analog systems, and then gradually transition to fully digital systems without the need to replace or modify site devices.

- Several communication devices (for example RS3 or the portable communication interface 268) can communicate simultaneously.

- The possibility of addressing transmitters makes it possible to connect up to 15 devices on the same pair of twisted wires.

- All transmitters of the "Intelligent Family" use a common message structure.

This allows interfacing devices to communicate in the same way with future or current products.

The "FIP" network is standardized in France by the Technical Union of Electricity or U.T.E. and the documents relating to this standard bear the references C46-601, PrC46-602, PrC46-603, PrC46-604, C46-605, PrC46-606, C46-607, C46-637, and C46-645.

The standardized industrial local network "FIP" is much faster and more complete than the "HART" network and above all it is standardized. Rosemount smart sensors are very efficient and the installed base considerable.

However, there are still too few sensors compatible with the "FIP" network. The problem to be solved therefore consists in making an adapter which allows the use of "HART" sensors on the "FIP" network.

There is currently no such adapter. The most widespread solution consists in using the standard 4-20 mA output of the "HART" sensors by connecting it to the input of an analog-digital converter itself connected to the network. The implementation of "intelligent" functions is impossible remotely. The user must move with a configuration tool (the portable communication interface 268) to act on these functions: calibration, range change, etc. ..

The local network can also be a "PROFIBUS" type network as described in the article entitled "Kommunikation auf der Instrumentierungsebene" by Walter Borst (Elektronik, vol. 40, number 20, October 1, 1991, pages 82-86, XP 000265899).

The solution envisaged by the creators of the "HART" protocol is obviously different. There is an industrial local network "HART" capable of implementing all the functionalities of compatible sensors and actuators.

This "HART" network is little used because it has the following drawbacks:

- it is slow (1200 bit / s) compared to the "FIP" network (1Mbit / s); - it is a "proprietary" network, therefore not standardized, with the well-known drawbacks of this type of network: limited competition, therefore high prices, catalogs also limited, no guarantee of durability, etc.

The object of the invention is to establish communication between a local network for example "FIP" or "PROFIBUS" and the sensors and actuators for example "FIP" or "PROFIBUS" as well as with the sensors and actuators " HART. Statement of the invention

The present invention relates to a device for adapting sensors or actuators of the "HART 'type with an industrial local area network, characterized in that it comprises a first stage of galvanic isolation, a filter amplifier, a formatting discriminator, a modem restoring the coded digital information, a microcontroller programmed to translate the messages into the language of the local network, an interface circuit and a second stage of galvanic isolation Advantageously the local network can be a "FIP" network or a "PROFIBUS" network .

The present invention also relates to a method for implementing this device, comprising the following steps:

- initialization of the serial link at 1200 Bauds; - loading of the interface circuit program;

- reading of fixed information from the sensor;

- reading of orders arriving via the local network;

- decoding of orders received by the local network, translation and transmission of a "HART" frame; - reading of the sensor variables.

Advantageously, the steps for reading sensor data include the following sub-steps:

- transmission of a frame after parity calculations and compaction; - reception of a frame;

- reading and analysis of the frame received after unpacking.

Thanks to the presence of the adapter devices of the invention which serve as interpreters, the sensors and actuators are "seen" in the same way by the network user. The implementation of all sensors and actuators compatible with the "HART" protocol becomes possible. All the digital information produced by a sensor passes through the local network. All intelligent functions can be operated from any point on the network. Brief description of the drawings

- Figure 1 illustrates the object of the invention;

- Figures 2A and 2B illustrate the operation of the "FIP" network;

- Figure 3 illustrates the operation of a "HART 'sensor;

- Figures 4 and 5 illustrate the principle of coding information "HART;

- Figures 6 and 7 illustrate the adaptation device of the invention;

- Figures 8 to 10 show flowcharts of operation of the device illustrated in Figure 6;

- Figure 11 illustrates an example of application of the device of the invention.

Detailed description of embodiments

In the following description, a local network of the "FIP" type will be considered by way of example. As shown in FIG. 1, the device of the invention must make it possible to establish communication between an industrial local network "FIP" 10 and "FIP" sensors 11 and "FIP" actuator 12, as well as with sensors "HART 13 and actuator" HART 14.

Thanks to the presence of adapter devices 15 and 16 according to the invention, which serve as inteφretes, these sensors and actuators are "seen" in the same way by the network user. The implementation of all sensors and actuators compatible with the "HART protocol becomes possible. All digital information generated by a sensor travels through the" FIP "network. The exploitation of all intelligent functions can be done from n any point on the network.

The local industrial network "FIP" makes it possible to connect the automation components to each other by a single cable which adopts a bus structure. The first goal is to save on wiring compared to wire to wire links to a multiple input acquisition system. The media used are the shielded two-wire pair or optical fiber. The digital coding of the information makes it possible to improve the accuracy of the measurements. On the other hand, this coding is necessary to establish the two-way dialogue with the "intelligent" sensors and actuators.

The mode of access to the network is managed in the manner illustrated in FIGS. 2A and 2B, on which are represented a bus arbiter AB and stations ST1 .... STn.

The bus arbiter manages the communication. He knows the data transmitting stations and the frequency of each data. It can for example, as shown in FIG. 2A, give the right to speak to the station ST2. All stations listen. The stations ST1 and ST3 are here interested in the message sent by the station ST2, not the others.

As shown in FIG. 2B, the station ST2 transmits its message, the stations ST1 and ST3 receive it simultaneously. The bus arbiter proceeds to the next call in due course. The functionalities of the "FIP" network are very numerous and it is not possible to describe them here. As described above, this network is standardized in France by the Technical Union of Electricity.

Figure 3 illustrates a "HART" sensor.

In this figure are shown the following elements: - a temperature sensor 20;

- a converter of the analog signal into digital signal 21;

a memory of the detector module 22 with its coefficients and its characteristics; - a microprocessor 23 allowing linearization of the sensor, recalibration of the scale, damping, diagnosis, • use of physical units, communication;

a memory 24 of the electronic module with its set scale points and the configuration of the transmitter;

a module 25 for local zero and scale adjustments; - a converter of the digital signal into analog signal 26;

a digital communication module 27, for example of the Bell 202 type; the input 28 being a differential pressure input.

The microprocessor 23, incorporated into the sensor, constitutes

"intelligence" which brings new functions: linearization of the curve, change of scale, etc. The non-volatile memories 22, 24 store the settings, the coefficients and the characteristics of the module.

The output 29 of the pressure information is in analog form thanks to the digital-analog converter 26 which delivers a current varying from 4 to 20 mA. All of the digital information remains accessible in digital form and in both directions via the digital communication module 27 which supe suposes "1" and "0" on the output current.

FIGS. 4 and 5 illustrate the principle of coding the "HART" information, with the adapter 32 to the "FIP" network 33. The sensor or actuator 30 is supplied by a continuous supply 31 (usually 24 Volts). Depending on the value of the physical quantity measured by the sensor, a current having a value of 4 to 20 mA flows through the resistors R1 and R2. A weak sinusoidal signal i is supeφosed to this current. As represented in FIG. 5, a logic "1" consists of a sinusoid period at 1200 Hz, a logical "0" consists of a sinusoid at 2200 Hz of identical duration. Reference 34 corresponds to the accesses to other users.

The current output is not disturbed by these sinusoids because their mean value is zero. These frequencies correspond to the Bell 202 standard used in the United States to transmit logic signals over the telephone network. Bell 202 modem circuits exist and allow these frequencies to be transformed into "0" or "1" logic signals.

The sequence of bits forms bytes which are coded in ASCII.

A series of characters forms a message. The "HART" protocol provides for a number of standardized messages which constitute the questions and answers necessary for dialogue with the whole range of sensor-actuators.

The adapter device of the invention is illustrated in Figure 6, the references considered in Figure 4 being retained. This device includes a first galvanic isolation stage 35, a filter amplifier 36, a formatting discriminator 37, a modem 38 restoring the coded digital information, a microcontroller 39 programmed to translate the messages in "FIP" language, a " known FIP circuit 40 serving as an interface with the "FIP" network, and a second galvanic isolation stage 41. This adapter device collects at the terminals of R1 a voltage proportional to the current 4-20 mA, as well as the sinusoidal voltage previously described. The first galvanic isolation stage 35 allows the alternating current to be transmitted without allowing the DC to pass. These signals are very weak because the value of the resistance R1 must be chosen as low as possible. It is therefore necessary to amplify them. The amplifier 36 forms a bandpass filter in order to improve the signal to noise ratio.

The sinusoids V1 represented in FIG. 7A, are transformed into slots V2, represented in FIG. 7B, by the discriminator 37 then presented at the input of the modem 38. The latter reconstitutes the logical "1" and "0" and directs them to the serial input of the microcontroller 39.

This microcontroller can reconstruct the "HART" messages, decipher the content and translate it to make it available to the "FIP" network 33.

The dialogue also works the other way. That is to say from the microcontroller 39 to the modem 38, then from the modem 38 to the galvanic isolation 35. The message is then injected into the current loop and received by the sensor or the actuator 30.

The microcontroller 39 can exchange data with the "FIP" network 33 thanks to one of the integrated circuits specially designed for this network (for example the Fullfip circuits designed by Cegelec, Fipiu by

Telemechanics). The galvanic isolation 41, on the "FIP" side, is usually carried out with a transformer or an optical fiber.

The software installed in the microcontroller works as illustrated in FIGS. 8, 9 and 10. FIG. 8 illustrates the flowchart of operation of the program of the microcontroller, which comprises the following steps:

- initialization of the serial link at 1200 Bauds (module 50);

- loading of the program of the "FIP" circuit (module 51); - reading of fixed information from the sensor (module 52);

- reading of orders arriving via the "FIP" network (module 53);

- decoding of orders received by the "FIP" network, translation and transmission of a "HART" frame (module 54); - reading of the sensor variables (module 55).

FIG. 9 illustrates the flowchart of operation of a subroutine for reading the sensor data used for the modules 52 and 55. It comprises the following steps: - transmission of a frame after parity calculations and compaction

(module 56);

- reception of a frame (module 57);

- reading and analysis of the frame received after unpacking (module 58); the compaction corresponding to the transition from the 8-bit ASCII code to a compacted 6-bit code, the decompaction corresponding to the transition from the compacted 6-bit code to the 8-bit ASCII code.

FIG. 10 illustrates the flowchart analyze-command (module 54). The action considered corresponds to a letter R, M, A, F, U Each letter (tests 60 to 65) corresponds to an associated processing (modules 66 to 71).

This software therefore allows:

- reading the request transmitted by the "FIP" network; - sending the corresponding command to the sensor or actuator in "HART language;

- reading the response;

- translating the response and making the data available to the "FIP" network, which is responsible for automatically transmitting it. Application example

All current applications in automation can be envisaged (acquisition of measurements, regulation, supervision, maintenance of sensors, etc.).

FIG. 11 illustrates an example of use of the adapters in the field of maintenance. In this figure are shown a microcomputer 75, adapters 76, 77, 78 connected respectively to sensors 79, 80 and 81. From the microcomputer, it is possible to carry out:

- the measurements and the recording of the quantities measured by the sensors with the physical unit, the time constant, the percentage of the range, chosen remotely by the user;

- maintenance operations by reading the indications stored for this purpose in the sensor;

- sensor test operations (periodic or triggered by the operator);

- the edition of a newspaper with the time of the incidents, their nature, the cause, the remedy brought; - remote adjustment and calibration operations become possible using "manifolds" (these are remote-controlled valves). The network is responsible for transmitting control orders. It also informs other users of the unavailability of this sensor during the entire operation.

Claims

1. Device for adapting sensors or actuators of the "HART" type with an industrial local area network, characterized in that it comprises a first stage of galvanic isolation (35), a filter amplifier (36), a setting discriminator form (37), a modem (38) restoring the coded digital information, a microcontroller (39) programmed to translate the messages into local network language, an interface circuit (40), and a second galvanic isolation stage (41) .

2. Method for implementing the device according to claim 1, characterized in that it comprises the following steps:

- initialization of the serial link at 1200 Bauds (module 50);

- loading of the interface circuit program (module 51);

- reading of fixed information from the sensor (module 52);

- reading of orders arriving via the local network

(module 53)

- decoding of orders received by the local network, translation and transmission of a "HART" frame (module 54);

- reading of the sensor variables (module 55).

3. Method according to claim 2, characterized in that the steps of reading sensor data comprise the following substeps: - transmission of a frame after parity calculations and compaction (module 56);

- reception of a frame (module 57);

- reading and analysis of the frame received after unpacking (module 58).

4. Method according to claim 1, characterized in that the local network is a "FIP" type network.

5. Method according to claim 1, characterized in that the local network is a "PROFIBUS" type network.