KROHNE MFC-400 User Manual

Supplementary instructions

MFC 400

MFC 400MFC 400

Supplementary instructions Supplementary instructions

Signal converter for mass flowmeters

Description of Modbus interface

Description of Modbus interfaceDescription of Modbus interface

Electronic Revision: ER 1.0.3_ Modbus version 2.1.0_

CONTENTS

MFC 400

1 General information 4

1.1 Scope of the document..................................................................................................... 4

1.2 Scope of delivery............................................................................................................... 4

1.3 Modbus protocol interface ............................................................................................... 4

2 Technical data 5

2.1 General technical data .....................................................................................................5

2.2 Technical data of the Modbus interface (acc. to EIA/TIA standards) .............................. 5

3 Electrical connections 6

3.1 Modbus connection........................................................................................................... 6

3.2 Connection to Modbus bus ............................................................................................... 6

4 Establish RS485 connection 7

5 Modbus protocol 8

5.1 RTU frame format............................................................................................................. 8

5.2 Data representation ......................................................................................................... 9

5.2.1 8-bit values.............................................................................................................................. 9

5.2.2 16-bit values............................................................................................................................ 9

5.2.3 32-bit values............................................................................................................................ 9

5.2.4 64-bit values.......................................................................................................................... 10

5.3 Modbus Register Addresses .......................................................................................... 11

5.4 Supported Function Codes............................................................................................. 11

5.5 Error messages.............................................................................................................. 11

5.6 Device identification ....................................................................................................... 12

5.7 Diagnostics ..................................................................................................................... 13

5.8 Parameters..................................................................................................................... 13

5.8.1 Device Control....................................................................................................................... 14

5.8.2 Device Status......................................................................................................................... 15

5.8.3 Measurement values ............................................................................................................ 16

5.8.4 Measurement Status compliant with NAMUR NE 107 ......................................................... 16

5.8.5 Auxiliary Values..................................................................................................................... 17

5.8.6 Totaliser ................................................................................................................................ 17

5.8.7 Zero Calibration .................................................................................................................... 20

5.8.8 Density Calibration Coefficients ........................................................................................... 21

5.8.9 Density Configuration ........................................................................................................... 21

5.8.10 Filters .................................................................................................................................. 22

5.8.11 System Control.................................................................................................................... 22

5.8.12 Calibration Coefficients ...................................................................................................... 23

5.8.13 Modbus RS485 Communication Settings ........................................................................... 24

5.8.14 NAMUR NE 107 Variable Event Group(s)............................................................................ 25

5.8.15 Concentration 1................................................................................................................... 26

5.8.16 Concentration 2................................................................................................................... 27

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MFC 400

CONTENTS

6 Application sequences 28

6.1 Saving and restoring the configuration setting ............................................................. 28

6.2 Zero calibration .............................................................................................................. 29

7 Troubleshooting 30

7.1 No response to Modbus requests .................................................................................. 30

7.2 Communication errors ................................................................................................... 30

7.3 Responding with exception "Illegal Function"............................................................... 30

7.4 Responding with exception "Illegal Data Address" ....................................................... 31

7.5 Responding with exception "Illegal Data Value"............................................................ 31

8 Appendix 32

8.1 NAMUR NE 107 Event Group(s)...................................................................................... 32

8.2 NAMUR NE 107 status signals ....................................................................................... 33

8.3 Supported Modbus function codes................................................................................. 33

8.4 Number format............................................................................................................... 36

8.5 Glossary .......................................................................................................................... 36

9 Notes 37

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1 GENERAL INFORMATION

1.1 Scope of the document

These instructions are supplementary to the signal converter handbook. For all other data, use the relevant chapters of the handbook. If you do not have this document, please contact the nearest office or download them from the manufacturer's internet site.

1.2 Scope of delivery

The information in this supplementary manual only contains the data applicable to MODBUS communication.

The technical data in the handbook shall be valid in its current version, provided that it is not rendered invalid or replaced by this supplement.

1.3 Modbus protocol interface

The Modbus interface to the signal converter is implemented in the Modbus RTU communications protocol and is done in accordance with the specification and requirements of the "Modbus Protocol Specification V1.1b".

MFC 400

The physical electrical parameters of the Modbus specification are defined by the EIA/TIA-485 (RS485) standard and the "Modbus over Serial Line - Specification and Implementation Guide V1.02".

Both specifications can be obtained on the official website of the Modbus organisation: http://www.modbus.org

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MFC 400

TECHNICAL DATA 2

2.1 General technical data

Interface RS485, galvanically isolated

Baud rate 1200, 2400, 3600, 4800, 9600, 19200, 38400, 57600 or

Protocol Modbus RTU (available as a separate document on request)

Maximum participants on bus 32 per line, master included (may be extended by repeaters)

Coding NRZ bit coding

Address range 1...247

Transmission procedure Half duplex, asynchronous

Bus access Master / slave

Cable Screened twisted pair

Distances Maximum 1.2 km / 3937 ft without repeater (dependant on

115200 bps

baud rate and cable specifications)

2.2 Technical data of the Modbus interface (acc. to EIA/TIA standards)

Kind of signal transmission Differential, 2-wire topology

Maximum number of transmitter/receivers

Voltage range on converter input -7...+12 V

Maximum voltage on converter output 5V

Minimum voltage on driver output, max. load

Maximum input current (off state) -20...+20 μA

Receiver input voltage -7...+12 V

Sensitivity of the receiver -200...+200 mV

Receiver input resistance >12kΩ

Short circuit current < 250 mA

Termination / polarization resistors (if activated by factory)

>1.5V

diff

120 Ω / 560 Ω

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3 ELECTRICAL CONNECTIONS

3.1 Modbus connection

The signal converter is hooked up onto the bus using terminals C and D:

Terminals Description

D- Signal A (D 0)

D Signal B (D 1)

C- Common 0 V

C Not connected

Terminals A and B of the signal converter are dependant on the options selected at order. Refer to the standard handbook of the signal converter for connection details.

3.2 Connection to Modbus bus

The signal converter is designed to be connected as a slave device onto the 2-wire bus implementation of the Modbus serial physical layer definition.

MFC 400

In addition to the D0 and D1 signal lines the bus MUST ground reference point for the data signals.

For proper operation of Modbus in half duplex mode in single or multi-drop communication, it is recommended that a termination resistor is applied to both ends of the data line. The simplest form of termination is line-to-line resistor across the differential input.

In RTU mode the Modus protocol requires quiet periods on the communications bus for synchronisation. It is therefore important that the Modbus is not allowed to "float", i.e. unreferenced to 0 V, as this could lead to spurious signals due to noise pick-up. It is therefore necessary to employ biasing resistors at one point on the bus network.

MUST include a "Common" signal line to act as a

MUSTMUST

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MFC 400

ESTABLISH RS485 CONNECTION 4

To establish a RS485 connection with the signal converter, prepare the master device with the appropriate default settings or use custom parameters specified via display of the signal converter.

The Modbus RS485 settings can be found in the menu C6.8 of the display. The following parameters can be configured:

Parameter Legal values Default values Display Fct. No.

Slave address 1...247 1 C6.8.1

"Baude rate" 1200, 2400, 3600, 4800, 9600,

Parity Even, Odd, No Even Parity C6.8.3

Data format Big Endian, Little Endian Big Endian C6.8.4

Transmission delay

Stop Bits 1 Stop Bit, 2 Stop Bits 1 Stop Bit C6.8.6

19200, 38400, 57600, 115200 bps

0...0.04 [s] 0s C6.8.5

19200 bps C6.8.2

These settings can be changed via Modbus too. For further information refer to

Communication Settings

on page 24.

Modbus RS485

All devices connected to the bus, must have the same baud rate.

INFORMATION!

It is of great importance to ensure at the time of the procedure of devices addressing, that there are not two devices with the same address. In such a case, an abnormal behaviour of the whole serial bus can occur. It is then impossible for the master to communicate with all present slaves on the bus.

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5 MODBUS PROTOCOL

5.1 RTU frame format

Using RTU (Remote Terminal Unit) format, data is transmitted as 8 bit binary characters. There are no special characters to determine the start and end of a message frame. Synchronization is achieved by a minimum silent period of at least 3.5 character times before the start of each frame transmission and a maximum silent period of 1.5 character times between characters in the same frame.

The format of the query and response frames vary slightly depending upon the function code. The basic form is outlined below.

Command function Frame format Description

MFC 400

Silent period 3.5 x T All transmissions must be preceded by a minimum silent

Slave address 8bits This is a single byte slave address which is transmitted

Function code 8bits This is an eight bit code in the range of 1...255 although

Number of points or data bytes when required

8 bit byte count 16 bit address

n×8bits Number of points:

period of 3.5 x T, where T is the transmission time of a single character. This can be calculated from the baud rate, e.g. T = 572 µs at 19.2 kbps.

first and must be in the range of 1...247. Address 0 is reserved for a broadcast address which all slaves should recognise, and therefore requires no response.

only 126 functions exist as the codes 129...255 represent an error condition. An error condition occurs when the addressed slave does not accept the command, in which case it responds with the function code + 128, i.e. with its msb set to 1.

Register start address:Register start address: data to be returned, this field will contain the 16 bit start address of the register (or data) to be returned. Note that the signal converter uses protocol addresses. Therefore the register address listed is the actual number required in the Modbus command.

E.g:

E.g: to access input register 30006, the register start

E.g:E.g: address is 30006 = 0x7536.

Byte count:

Byte count: In general this is only present in frames that

Byte count:Byte count: are transferring data, and has a value equal to the number of bytes contained in the data field. The data field is limited to a maximum of 250 bytes.

Number of points: for a query command that requires data

Number of points:Number of points: to be returned, this field will contain the number of registers to be returned regardless of their bit size.

Data bytes:

Data bytes: contains the data requested. The signal

Data bytes:Data bytes: converter can use Big Endian format (MSB first) or Little Endian format (LSB first).

CRC 16 bits This field contains a 16 bit CRC which is calculated on all

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the data bits of the message bytes.

MFC 400

5.2 Data representation

There are two data types used to transmit information on a Modbus data bus, the "Bit" and the "Register". The "Bit" represents a single binary state, whether as an output or an input condition. The "Register" is a 16-bit integer transmitted as two 8-bit characters. Using multiple "Registers" the Modbus interface can transmit higher accuracy values such as "Floating Point" and "Double Precision Floating Point" numbers.

"Bit" variables are packed into a byte containing 8 bit, so each character, sent or received, can contain up to 8 "Bit" variables. The master and slave devices use only as many 8 bit data characters as are required to transmit the information. Any unused bits in the data characters are ignored. The bit that is requested by the start address is transmitted in the LSB at bit 0. The next "Bit" value is transmitted in the next bit (bit 1). This continues until the last bit location (bit 7) of the LSB is reached. The next "Bit" value is then transmitted in the next data byte (LSB+1/MSB) at bit 0. This continues until all of the requested values have been transmitted. Any unused bits in the MSB are filled out with "0"s.

For simple single register variables the MSB of the register is transmitted first, with the LSB following immediately after. However, for variables that require multiple registers, i.e. the "Floating Point" and "Double Precision Floating Point" variables, the transmission order can be selected in the RS485 settings. By default, those values will be transmitted in Big Endian.

MODBUS PROTOCOL 5

5.2.1 8-bit values

N 0x00 Byte

5.2.2 16-bit values

N MSB LSB

5.2.3 32-bit values

Little Endian

N LSB + 1 LSB

N + 1 MSB LSB + 2

Big Endian

N MSB LSB + 2

N + 1 LSB + 1 LSB

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5 MODBUS PROTOCOL

Float (single precision, IEEE 754)

MSB LSB + 1 LSB + 1 LSB

SEEEEEEE EMMMMMMM MMMMMMMM MMMMMMMM

With S = sign, E = exponent, M = mantissa/fraction

5.2.4 64-bit values

Little Endian

N LSB + 1 LSB

N + 1 LSB + 3 LSB + 2

N + 2 LSB + 5 LSB + 4

N + 3 MSB LSB + 6

MFC 400

Big Endian

N MSB LSB + 6

N + 1 LSB + 5 LSB + 4

N + 2 LSB + 3 LSB + 2

N + 3 LSB + 1 LSB

Double (double precision, IEEE 754)

MSB

MSB LSB + 6

MSBMSB

SEEEEEEE EEEEMMMM MMMMMMMM MMMMMMMM

LSB + 3

LSB + 3 LSB + 2

LSB + 3LSB + 3

MMMMMMMM MMMMMMMM MMMMMMMM MMMMMMMM

LSB + 6 LSB + 5

LSB + 6LSB + 6

LSB + 2 LSB + 1

LSB + 2LSB + 2

LSB + 5 LSB + 4

LSB + 5LSB + 5

LSB + 1 LSB

LSB + 1LSB + 1

LSB + 4

LSB + 4LSB + 4

LSB

LSBLSB

With S = sign, E = exponent, M = mantissa/fraction

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MFC 400

5.3 Modbus Register Addresses

The signal converter supports four types of data references, which are associated to a range of Modbus registers.

Address range Primary tables Access rights

0...9999 Coils read + write

10000...19999 Discrete Inputs read

20000...39999 Input Registers read

40000...65535 Holding Registers read + write

INFORMATION!

•

Sometimes register numbers are asked for. The register numbers can be calculated by adding a 1 to the register address.

•

Some systems cannot use addresses above 9999. For these systems there is the possibility to use the listed addresses but

- for Input Registers omit the leading 3 of 3xxxx;

- for Holding Registers omit the leading 4 of 4xxxx.

MODBUS PROTOCOL 5

5.4 Supported Function Codes

Function code Name

dec hex

01 01 Read Single Coil

02 02 Read Descrete Inputs

03 03 Read Holding Register

04 04 Read Input Register

05 05 Write Single Coil

08 08 Diagnostics

16 10 Write Multiple Register

43 2B Encapsulated Interface Transport

For detailed information about the telegrams structure of all function codes refer to

Modbus function codes

on page 33.

5.5 Error messages

When the signal converter detects an error in the requests, received in a properly formatted telegram, it will respond with an error message. The error message response telegram is formatted as follows:

Supported

Address Function Code Error Code CRC Lo CRC Hi

The msb (most significant bit) of the requested function code is set (add 0d128 / 0x80) in the reponse telegram to indicate an error has been detected. For example, if an error were detected in a function 1 request, then the returned function code would be 0x81 (0d129).

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5 MODBUS PROTOCOL

The single data character in the response telegram will indicate the type of error detected. These are as follows:

MFC 400

Error

Name Meaning

Code

01 ILLEGAL FUNCTION The requested function code is not supported or not valid due to the

02 ILLEGAL DATA

03 ILLEGAL DATA VALUE The requested data is invalid for the register being written.

04 SLAVE DEVICE

06 SLAVE DEVICE BUSY The slave is unable to process the requested command because a

ADDRESS

FAILURE

Errors due to communications faults (CRC errors, Parity errors etc.) are logged but no response is returned because the data in the received telegram is deemed unreliable. The master system can read the error logs by using the diagnostics command (for details on Function Code 0x08 refer to

Diagnostics

on page 13).

5.6 Device identification

Retrieve all of the identification information from the signal converter.

Modbus Function Code "Encapsulated Interface Transport" (0x2B).

current settings of the device.

The register requested is not valid or the quantity of requested registers hits invalid registers.

An unrecoverable error occurred while the slave was attempting to perform the requested action.

long-duration command is in progress. The master should retransmit the message later.

Modbus Encapsulated Interface (MEI) type (0x0E).

Category Object IdObject name Type Content

Basic 0x00 VendorName 16 byte ASCII String KROHNE

0x01 ProductCode 10 byte ASCII String CG number; order code for the

0x02 MajorMinorRevision 7 byte ASCII String Electronic Revision number

Regular 0x03 Vendor URL 32 byte ASCII String www.krohne.com

0x04 ProductName 16 byte ASCII String MFC400

0x05 ModelName 16 byte ASCII String Modbus

0x06 UserApplicationName 16 byte ASCII String User tag, displayed on the

signal converter assembly

header of the local screen

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