KROHNE MFC85 User Manual

CORIMASS

Instructions to use with

Krohne SMART or HART

MFC 081 / 085 Mass Flow Converters

KROHNE SMART HART

Instruction Manual

Communications Protocol

and

Hart is a registered trademark of the HART Communication Foundation

Contents

1. The Krohne SMART System 3

1.1 Description of Operation 3

1.2 SMART overview 3

1.3 Connecting the PC or Hand-held Communicat or 4

1.4 PC CONFIG Software Package 5

1.5 Further Instruction Manuals 5

2. The HART

Protocol 6

2.1 Method of Operation 6

2.2 Point to point O perati on 6

2.3 HART

Protocol Structur e 7

2.4 Hand-held Communi cat or 9

1. The Krohne SMART System

1.1 Description of oper at ion

The interface for the Krohne Smart system is the current output. Bi - di r ecti onal inform at ion can be transmitted via the current output cables. The current output signal (0/4 to 20 mA is not affected because the mean value of the signal containi ng the digit al informati on is equal to zero.

The signals are superimposed by means of frequency shift keying (FSK), based on the Bell 202 comm uni cat ion standard. The digital t r ansmission signal is form ed from two frequencies: 2200 Hz = “0” and 1200 Hz = “1”.

MEASURED VALUE

0 mA 0 mA

TIME TIME

CONVENTIONAL SMART FSK MODE

MEASURED VALUE

20 mA20 mA

2200 Hz

“0”

1200 Hz

“1”

The Smart technology will enable you to utilize its advantages for initial start up, maintenance work and to change settings. All parameters for new measuring devices (in this case, the mass flow m eter or m eters) or those to be changed can be defined and entered into the PC in the workshop. The stored data can then be downloaded to the mass flow meter and started up from t he control r oom (via the cable marshal l ing rack).

The same applies to operation and maint enance. The status of the mass flow meter can be displayed on-line, or in t est mode, the current output can be set t o a specific val ue or values in order to test the whole circuit. If a converter is r eplaced, the parameter set from the data base (PC) can be downloaded into the new converter. Thi s elimi nates tim e consuming data entry and programming. The possibility of errors being incurred during programming is also eliminated.

1.2 SMART overview

All Krohne Smart si gnal converters may be operated via PC. The transmission route m ay be up to 1600 m / 5250 f t long. The load between the coupling part of the PC and the converter output loop should be at least 100 ohms.



Note: This protocol is not compatibl e with HART

even though it uses a similar method of

comm unication.

MFC 081/085

SMART

0/4 - 20 mA + FSK

LOAD

SMART Converter

AdaptorMIC 500

Data can be transferred between a PC and MIC 500 or vice versa

CONFIG Program communicates directly with converter

1.3 Connecting the PC

The PC can only be connected to the first current output of the MFC 081/085, i.e. current output from terminals (5 (–) and 6 (+). The other current outputs that may be available (depending on options ordered) will not carry the FSK signal and the Smart syst em will not work. If another comm unication protocol option has been ordered, e.g. RS 485 or Profibus, then the Smart system will be inactive as the processor will only accommodate one comm uni cation protocol at a time.

–

5 6 4

4.1

4.2

MFC 081/085

0/4 - 20 mA

Smart always available on first current output only

Note:

This communi cation protocol is a Krohne designed protocol and for use with Krohne CONFIG Software package and not intended for use on non-Krohne equipment. The protocol description is thus al so not available for distribution.

1.4 PC CONFIG Software package

The VDI/VDE-GMA 2187 Guideline issued in Germany is the fi rst attem pt to define a mode of operation for signal converters incl uding those of different makes. The operating unit is t he PC through which the all Krohne Smart converters can be controlled and programmed. The signal converters are linked via a RS 232 interface at the PC. All Krohne Smart transducers can be operated using the Krohne PC “CONFIG” operator package.

Mini mum PC requirement s

•

PC, personal computer, with MSDos or com pat ible operating system

•

Disk drive: 3½”

•

Screen mode with 25 × 80 characters

•

Serial interface RS 232

•

No special requirements imposed on graphic adaptor (Hercules, EGA, VGA, etc.), the CONFIG program operates in the text mode so older PC’s can also be used.

Items suppl ied with Krohne PC operator package CONFI G

•

1 × 3½” diskette with complete CONFIG software

•

Smart converter or RS 232 adaptor ( or RS 232 - RS 485 converter on request)

•

Smart cable, link between current output and Smar t converter

•

Adaptor for 25-pi n RS 232 int erface at PC

Screen layout, operator control and functions

•

Operation via m ouse or keyboard and hot keys

•

Screen layout and operator control modelled on the Microsoft Windows user interface

•

Connection set-up to Smart signal converters or the MIC 500 hand-held communicator

•

Diagnostics, detailed presentation of signal converter messages, and call of simulation functions (tests)

•

Change, compare, print and store inst r ument parameters

•

Dynamic representation of m easured values and signal converter status

1.5 Further Instruct i on Manuals

Krohne PC CONFIG Operating Manual Order No. 7.02196.71.00 These manuals should accompany t he equipment when ordered.

2. The HART® Protocol

2.1 Method of O per at i on

The HART on the Bell 202 [1] communication standard. The digital signal is made up from two frequencies - 1200 Hz and 2200 Hz, representing bits 1 and 0 respectively. Sine waves of these frequencies are superimposed on the DC analog signal cables to give simultaneous analog and digital communi cations. Because the average value of the FSK signal is always zero, the 4 - 20 mA signal is not af f ected.

This produces genuine, simult aneous communication wit h a response time of approximately 500 ms for each field device, without interrupting any analog si gnal t ransm issi on that m i ght be taking place.

Up to two master devices may be connected to each HART generally a management system or a PC while the secondary one can be a hand-held terminal

or laptop com puter. A standard hand- held terminal - called the HART available to make field operations as uniform as possible. Further networking options are provided by gateways.

approx. +0.5 mA

protocol operates using the frequency shift keying (FSK) principl e, which is based

loop. The primary one is

Communicator - is

analog signal

approx. +0.5 mA

1200 Hz

“1”

2200 Hz

“0”

Simultaneous analog and digital signals

Because the mean harmonic signal value is zero, digital communi cation makes no diff erence to any existing analog signal as demonst r ated in the figure above.

2.2 Point to point oper ation

The figure below shows some examples of point-to- point mode. The conventional 4 - 20 m A signal continues to be used for analog transmission while measurement, adjustment and equipment data is tr ansf erred digi t ally.

The analog signal remains unaffected and can be used for control in t he normal way. HART

data gives access to maintenance, diagnostic and other operational dat a.

Analog

HART interface

Digital

Up to 2 updates/sec

MFC 081/085

Multiple Masters

2.3 HART

HART the International Or gani sat ion for Standardisat i on ( ISO) [3]. The OSI model provides the

structure and elements of a communication system. The HART

Protocol Structure

follows the basic Open Systems Interconnection (O SI) r eference model, developed by

protocol uses a reduced OSI

model, implementing only l ayers 1,2 and 7.

OSI Reference Model

Open Systems Inte rconnecti on

Layer Function

7 6 5 4

Application provides formatted data HART instructions

Presentation converts data

Session handles the dialogue

Transport secures the transport

connection

Network establishes network

connections

Link establishes the data

link connection

Physical connects the equipment Bell 202

HART

HART protocol

regulations

The

protocol implements layers 1,2 and 7 from the OSI model

HART

Layer 1, the Physical layer, operates on the FSK principle, based on the Bell 202 comm uni cation standard:

Data transfer rate: 1200 bit/s Logic ‘0’ frequency: 2200 Hz Logic ‘1’ frequency: 1200 Hz

The vast majority of existing wiring i s used for t his type of digital communi cat ion. For short distances, unshielded, 0.2 mm 1500 m), si ngle, shielded bundles of 0.2 mm distances up to 3000 m can be covered using single, shielded, twisted 0.5 mm

two-wire lines are suitable. For l onger dist ances (up t o

twisted pairs can be used. Beyond this,

pairs.

A minimum resistance of 230 ohm s must be available in the communication ci r cuit.

Layer 2, the Link layer, establishes the format f or a HART

message. HART® is a master/slave protocol . Al l the communication activiti es origi nat e from a master, e.g. a di spl ay terminal. This addresses a field device (slave), which interprets the command message and sends a response.

The structure of these messages can be seen in the figure below. In multi-drop mode this can accomm odat e the addresses for several field devices and terminals.

Structur e of a HART

Preamble SD AD CD BC Status Data Parity

message

Field device and communication status (ONLY from field device to master)

Byte count HART instruction Display termi nal and f ield device

addresses Start character

The HART message structure offers a high degree of data integrity

A specific size of operand is required to enable the field device to carry out the HART instruction. The byte count indi cat es the number of subsequent status and data bytes.

Layer 2 improves transmission reliability by adding the parity character derived from al l the preceding characters; each character also receives a bit for odd parity.

The individual characters are: 1 start bit 8 data bits 1 bit for odd parity 1 stop bit

Layer 7, the Application layer, bri ngs t he HART instructi on set int o play. The master sends messages with requests for specified values, actual values and any other data or param eters available from the device. The field device interprets these instructions as defined in the HART protocol. The response message provides the master with st at us i nf or mation and data from the slave.

To make interaction between HART compatibl e devices as efficient as possible, classes of conformi t y have been established for masters, and classes of commands for sl aves. There are six classes of conformity f or a master as seen in the figure below.

Classes of instructi on and classes of conformi ty

Read Measured

UNIVERSAL

COMMANDS

Variable

Read Universal

Information

COMMON

PRACTICE

COMMANDS

DEVICE

SPECIFIC

COMMANDS

For slave devices, logical, unifor m communication is pr ovi ded by the followi ng command sets:

Universal commands

understood by all field devices

Common pr act ice commands

provide functions which can be carried out by m any, though not all, f ield devices. Together, these commands compr ise a library of the most common fi eld device functions.

Device-specific commands

provide functions which are restricted to an individual device, permitting special features to be incorporated that are accessible by all users.

Write Standard

Parameters

Read Device-Specific

Information

Write Selected

Parameters

Read and Write

Entire Database

Examples of all three command sets can usually be found in a field device, including al l universal commands, some common-practice commands and any necessary device-specific comm ands.

2.4 Hand-held Communicator

A standard HART operating instructi ons for this communicator i s not supplied by Krohne and should accompany the hand-held communi cat or when purchased.

A HART requested DDL’s already downloaded to the instrument.

The Krohne CONFIG software package can also be supplied for HART instrum ents. The functi ons ar e similar to that described in Sect. 1.4 (available end 1996).

Further information on HART book available on request.

The Corimass MFC 081/085 HART require any further inform at ion, please contact your nearest Krohne office or Product Management in Duisburg, Germ any.

Communi cat or is available from Kr ohne and m ay be purchased with all cust omer

hand-held comm unicator may be used on Krohne equipment. The

compatible

may be found in the HART® Field Comm uni cation Protocol

protocol is avai lable from Krohne on request. Should you

Krohne RS 485 Bus-Protocol

Pages 11-23

Contents

1. General 12

2. Technical Specifications 12

3. Connecti on of i nst r uments on the BUS system 13

3.1 Single Master/Slave configuration (Non Ex applicati ons onl y) 13

3.2 Single Master/Slave configuration (Ex applicati ons) 13

3.3 Multi-drop appl i cat ions 14

3.4 Bus terminati on 14

3.5 Network Biasing Resistors 15

4. Using t he Cur r ent out put with the RS 485 Bus 16

5. Convert er configuration 17

6. Transmission format 18

7. Format of the data field 18

8. Format of the data bl ocks 19

8.1 Measurement Block 19

8.2 Error list 20

9. Refer ence documentation 21

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