KROHNE MFC-010C User Manual

OPTIMASS

MFC 010 Converter

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Contents

1. Introduction 5

2. Mechanical Installation 5

3. Electrical Installation 6

3.1 Electrical Input Specifications for the MFC010 6

3.2 Recommended Cable Specification 7

3.3 Connection to the MFC010 8

3.4 Connection to the Modbus Bus 10

3.5 Installation Guidelines for Electromagnetic Compatibility 12

4. Installation in Hazar d o u s Area Applications 13

4.1 Power Supply Barrier Devices 15

4.2 Modbus Barrier Devices 16

4.3 Connection To The Modbus Bus 17

5. Modbus Protocol Interface 19

5.1 Character Transmission Format 19

5.2 Modbus Telegram Format 20

5.3 Data Types in Modbus 20

5.4 Multidrop Operation 21

5.5 Calculating Data Transmission Rates 21

5.6 Error Messages in Modbus 22

6. Modbus Functions Supported by the MFC010 23

6.1 01 (0116): Read Coil Status 23

6.2 02 (0216): Read Discrete Input 24

6.3 03 (0316): Read Holding Registers 25

6.4 04 (0416): Read Input Registers 26

6.5 05 (0516): Force Single Coil 27

6.6 06 (0616): Preset Single Register 28

6.7 07 (0716): Read Exception Status 29

6.8 08 (0816): Diagnostics 30

6.9 11

6.10 16

(0B

): Fetch Comm. Event Counter 30

(10

): Preset Multiple Registers 31

6.11 17 (1116): Report Slave ID 32

7. MFC010 Modbus Data Model 33

7.1 MFC010 Register Structure 33

7.2 Discrete Status Output “Coil” Registers 39

7.3 Discrete Input (Binary) Status Registers 41

7.4 Input Registers 43

7.5 Holding Registers 49

8. MFC010 Operations 71

8.1 Mass Flow Zero Calibration 71

8.2 Density Calibration 72

8.3 Fixed and Referred Density Operation 75

8.4 Concentration Measurement 76

8.5 Using the System Protection Passwords 76

8.6 Saving and Restoring Configuration settings 77

8.7 Implementing User Defined Units 77

8.8 Using the Internal Process Control Mechanism 78

8.9 Custody Transfer Applications 78

8.10 Pressure Suppression 79

MFC010 Interface Manual

9. Error and Warning Messages 81

9.1 System Errors 81

9.2 Process Warnings 85

10. Trouble Shooting 88

10.1 “No Response to Modbus Requests” 88

10.2 “Communication Errors” 88

10.3 “The MFC010 is responding with an Illegal Modbus Function Message” 89

10.4 “The MFC010 is responding with an Illegal Data Message” 89

10.5 “The MFC010 is responding with an Illegal Address Message” 89

Appendix A : Modbus CRC Checksum Calculation 90 Appendix B : Hexadecimal and Binary Notation 92 Appendix C : Decoding Floating Point Numbers 93

Single Precision Floating Point Numbers (“Floats”) 93 Double Precision Floating Point Numbers (“Doubles”) 94

Appendix D : Sensor Sizes and Associated Default Register Setti n g s 95 Appendix E : Installation of Power Supplies in MFC010 Applications 97 Appendix F: MFC010 Toolbox 100

Product Liability and Warranty

The MFC010 mass flow sensor electronics are an integral part of the OPTIMASS a nd OPTIGAS m ass flowmeter families des igned f or t he direct measurement of mass flow rate, product density and product temperature, and also indirectly enables the measurement of par ameters s uch as m ass t otal, concentration and volume flow.

When used in hazardous areas, special codes and r egulations are applicable which are specified in the section on H azardous ar ea appl ications i n t his doc ument. Please note t hat haz ardous area approved meters must ALWAYS be c onnected using appropriate barriers, even when used outside the hazardous area, else the approval is void.

Responsibility as to suitability and intended use of the equipment rests solely with the purchaser. KROHNE does not accept any liability resulting from misuse of the equipment by the customer.

Improper installation and operation of the flow meters may lead to loss of warranty. Warranty is also null and void if the instrument is damaged or interfered with in any way.

In addi tion, t he “ General C onditions of S ale”, w hich f orm t he bas is of t he pur chase agr eement, are applicable.

If you need to return OPTIGAS or OPTIMASS flow meters to KROHNE, please complete the form on the last page of the Sensor manual and return it with the meter to be repaired. KROHNE regrets that it cannot repair or check returned equipment unless accompanied by the completed form.

Standards and Approvals

The M FC010 c onverter i s t ested and c ertified, w hen i nstalled according to the directions contained i n t his doc ument, t o m eet al l of the r equirements of t he E U-EMC a nd PED directives and hence bears the CE symbol.

The MFC010 c onverter in association with the OPTIGAS and O PTIMASS s ensor systems is approved f or oper ation i n H azardous ar ea i nstallations according to the harmonized European Standards (ATEX).

Approvals for Hazardous area i nstallations c ompliant w ith t he F M and C SA standards are pending.

Copies of all of the certificates of conformity f or t he appr ovals l isted abov e ar e av ailable f rom t he download centre of the KROHNE website at www.krohne.com.

THE CONTENT OF THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT PRIOR NOTICE.

MFC010 Interface Manual

1. Introduction

The MFC010 is a s tand al one s ignal c onverter des igned t o di rectly i nterface t he O PTIMASS and OPTIGAS f amilies of C oriolis m ass f lowmeters into c ontrol s ystems us ing t he M odbus R TU protocol where t here i s no r equirement f or t he ex tensive out put c ontrol features provided by more expensive converter solutions.

The MFC010 performs three primary direct measurements, Mass flow, Density and Temperature. Using these primary measurements the MFC010 is able t o c alculate an ar ray of s econdary v alues s uch as Volume Flow, Velocity and Concentration.

Mass Flow – Mass flow measurement doesn’t come any simpler, once installed just perform a “ Zero

Calibration”, “ Reset” t he “ Totalisers” and aw ay y ou go. W here P rocess noi se i s a nui sance use the “Measurement T ime C onstant”, “ Low F low T hreshold” and “ Pressure S uppression” features to provide reliable and repeatable results.

Density – Using the inverse relationship between the Density of the process product and the oscillation

frequency of the measuring tube, the MFC010 can provide a v ery accurate and r eliable Density reading. In or der t o m aximise t he ex cellent per formance o f the MFC010 the user s hould per form a dens ity calibration after installation. T he MFC010 provides t wo forms of Density C alibration, the simple “Single Point Calibration” and t he more accurate “Two Point Calibration”. U sing the “Density Averaging” feature

the user can reduce noisy readings caused by process installation and noise. NB. Density measurement

is not available with the OPTIGAS 5000 meters.

Concentration – Using the “Density” and “Temperature” m easurements t he M FC010 i s c apable of

calculating the concentration of a pr oduct in the pr ocess medium, from one of a num ber of pre-defined industry standards, such as “ °Brix” a nd “ °Baumé”, as w ell as us er def ined m ixtures us ing t he programmable coefficients. Concentration measurement is a f unction that comes with a c omprehensive manual and a Coefficient calculation software package w hich will take the users own process data and convert it into compatible coefficients to permit the MFC010 to automatically calculate the concentration of the target process.

Velocity – Using the measured mass flow and density, the velocity of the product is calculated using the

“Pipe Diameter” setting. By default this is set to the measuring tube internal diameter to calculate the velocity of the product passing through the sensor, but it can be set to calculate the velocity in a section of the connecting pipe work.

Process Control – Where precise process conditions are required, the “Process Control” function can be

used t o det ect adv erse v ariations i n t he “ Density” or “ Temperature” m easurements and, as well as indicating the condition, it can take one of a num ber of pr edefined ac tions ac cording t o t he us ers requirements.

2. Mechanical Installation

Refer t o t he i nstallation gui delines and i nstructions f or m ounting t he s ensor i n t he process pipe work provided in the handbook on the CD supplied with the sensor.

MFC010 Interface Manual

3. Electrical Installation

The MFC010 is provided with four electrical terminal connections.

V+ The power supply input terminal.

V- The power supply return path and “Common” for the Modbus interface.

A The inverting (RS485-) terminal for the Modbus interface.

B The non-inverting (RS485+) terminal for the Modbus interface.

These terminals can be accessed in the terminal compartment of the sensor.

3.1 Electrical Input Specifications for the MFC010

NB all voltages, unless otherwise stated, are with reference to the “V-” terminal.

V+ Terminal

Min. Input Voltage 11.4V DC

Max. Input Voltage 12.6V DC

Max. Input Current 200mA DC

A & B *

Min. Input Voltage -7V DC

Max. Input Voltage +11.8V DC

Min. Output Voltage -6V DC

Max. Output Voltage +6V DC

*The M odbus pr otocol r equires t hat t he c ommunications i nterface t o t he MFC010 complies with the limitations of the EIA/TIA-485 (RS485) specification.

For a standard, non hazardous area, sensor the input impedance of the MFC010 is equivalent to 1/8 of a standard RS485 load, i.e. an input impedance of >96kΩ, permitting it to be connected to the Modbus bus in accordance with the Modbus requirements. However, when installed in a Hazardous area the MFC010 requires that suitable barrier devices must be fitted between the MFC010 and the Modbus main bus, see sections 4.1 & 4.2 for det ails of s uggested bar rier devices and c onnection. I f t he main Modbus Bus is configured f or m ultidrop oper ation, a M odbus c ompatible R S485 r epeater i s r equired to connect the barrier devices to the bus, see section 4.3 for further details.

3.2 Recommended Cable Specification

The c able us ed t o c onnect t he M FC010 t o t he M odbus m aster c ontrol s ystem should be an overall screened t wisted pai r c able, w ith t wo t wisted pai rs of a m inimum 20 AWG conductor. The total cable capacitance s hould not ex ceed 50nF and t he c onductor inductance should not exceed 200μH. The external cable insulation should be specified appropriately for the environment into which the device is to be installed. The outside diameter of the cable should be between 6.5 mm and 9.5 mm to ensure proper sealing is achieved when passed through the cable gland entry.

KROHNE c an supply suitable cable that can be or dered to the required l ength, the part numbers are as follows

External Insulation Colour Grey - KROHNE Part No. X5871059989

External Insulation Colour Blue - KROHNE Part No. X5871069989 (For hazardous area installations)

The maximum cable length from the MFC010 to the bus “Master” device is 300m when using the default Modbus transmission speed of 19200 Baud. There are further limitations on the cable length when installing the system into a Hazardous area, refer to section 4.3 on page 17 for details.

MFC010 Interface Manual

Terminal

Input Connection

12V

V+ - V-

A (RS485-)

B (RS485+)

3.3 Connection to the MFC010

1. Unscrew the fixing screw on the junction box cover.

2. Release the two fixing screws holding the cable grip in place and remove the grip.

3. Strip approx. 50mm/2” of the outer casing of the signal cable.

4. Split the screen away from the cores and fold it back on the outer cable.

5. Fit the cable grip and secure, making sure that the screen is gripped under the grip.

6. Connect the four cores to the terminals marked A,B, 12V, - as shown

NOTE: The spring loaded connections are released by depressing the white lever above each connection

1 Cable Gland 2 Cable Grip/Earth 3 Terminal connections 4 Jumper for EOL resistor (not supplied) – off in position as shown, on in other position

MFC010 Interface Manual







3.4 Connection to the Modbus Bus

The MFC010 is designed to be connected as a Slave device onto the 2-wire bus implementation of the Modbus physical layer definition. In this configuration the receiver and transmitter lines for each device are c onnected t ogether, Transmitter A t o R eceiver A and T ransmitter B t o Receiver B, and operated in Half Duplex mode, where the master transmits a request and only after receiving it does the nominated slave device transmit a reply. When not responding to a direct request from the Master device, the Slave devices r emain passive, m onitoring the bus and aw aiting a suitable request from the Master device. In addition to the A and B signal lines the bus MUST include a “Common” signal line to act as a ground reference point for the A and B signals.

The m aster bus m ust be t erminated at i ts phy sical end poi nts by suitable termination networks connected between the A (D0) and B (D1) signal lines. When not using bus-biasing resistors, see next paragraph, each termination network may consist of a single 150 O hm, 0.5W r esistor. H owever, when bus-biasing resistors are required, a more suitable termination network would consist of a 1nF capacitor in series with a 120 Ohm, 0.25W resistor. NB It is common that the Host system “Master” is physically at one end of the bus, so one of the termination resistors is fitted at its terminals, but it should be r ealised that this is not always the case and care should be taken to ensure that the termination network is at the physical end of the bus. In a point-to-point configuration, when only one Slave device is fitted to the bus, then the terminating networks can simply be situated at the connecting terminals of the master and s lave devices.

Some slave devices require that Bus-Biasing resistors are fitted to ensure that the bus is in a defined state w hen none of t he t ransmitting devices are active. The MFC010 does NOT require Bus-Biasing resistors t o be f itted but is compatible with their presence on t he bus i f one or more of the other slave devices on the bus require them to be fitted, as long as they comply with the Line Polarization requirements of the Modbus specification.

In a m ultidrop bus c onfiguration t he s lave dev ices ar e c onnected t o t he m ain bus cable by branch connections at intervals along the length of the main bus. T he branch connections, Derivations as they are termed in the Modbus specification, must be l ess than 20m in length from the main bus cable to the slave device. Some slave devices permit direct connection to the main bus, known as “Daisy Chaining”, in some cases by providing extra terminals and c able ac cess poi nts. H owever, as i ndicated i n t he previous s ections, ac cess t o t he t erminal c ompartment of t he M FC010 i s limited; therefore i t i s not practical to directly connect the MFC010 to the main bus. Instead, the installation should utilise a short branch c onnection. I f a greater length of cable is required between the MFC010 device and the main Modbus bus, the user should install a suitable RS485 repeater between the MFC010 and the bus (refer to the diagram below).

Because the connection to the bus requires exposing the signal wires, t he connection to the main bus should be made within a suitable EMI shielded enclosure. This connection should include the “Common” signal connection, the power supply connection (if a suitable one is provided by the bus), and the drain wire when available. Each of the cable screens must be properly terminated to the enclosure by means of appropriate EMC cable glands. For example:

If t he Bus does not provide a s uitable power s upply for the MFC010, a separate suitable power supply connection should be made at this point.

An RS485 Repeater can be used to extend the length of the Bus and the number of slave devices that are attached t o t he bus ( refer t o t he f igure bel ow). H owever, if the bus is extended in such a fashion, termination and polarization networks should be fitted according to the same rules as used for the main bus (see descriptions above).

MFC010 Interface Manual

NB For H azardous A rea appl ications t he us er s hould r efer t o s ection 4.3, on page 17, f or c onnection

details.

NB For multidrop systems, ensure cycle times are properly calculated to ensure bus speeds are adequate

for the application.

3.5 Installation Guidelines for Electromagnetic Compatibility

Whilst t he M FC010 and i ts as sociated s ensor has been des igned, t ested and c ertified t o m eet the requirements on international s tandards of E lectromagnetic C ompatibility ( EMC), i t i s t he us ers responsibility to ensure that the connection guidelines described in this document are followed. In addition the user should use recognised good practise in the location and cable routing of the MFC010 in relation to its surrounding environment. The us er should consider t he following suggestions w hen installing an MFC010 into a system.

1. Every effort should be made to avoid significant lengths (>50mm) of unshielded signal wire when connecting to the system, any terminal connections should be housed in a suitably shielded enclosure.

2. Avoid routing the cable in groups with or alongside other power carrying cables.

3. Avoid locating the MFC010 or routing the connection cable in close proximity to large electrically powered equipment, such as pumps, inverters etc.

4. If necessary, route the connection cable through a suitably earthed metal conduit.

4. Installation in Hazardous Area Applications

Before installation the user MUST ENSURE that the equipment to be installed is the Hazardous ar ea approved equipment.

Copies of the appropriate certificates can be found on the KROHNE website at www.krohne.com.

Before installation the user MUST refer to the hazardous area installation document, supplied w ith this equipment, and strictly adhere to the relevant installation instructions indicated therein.

When the MFC010 is used in Hazardous area installations, suitable barrier devices MUST be fitted. The Safety Parameters for the MFC010 are as follows. All interface and barrier devices must be appropriately certified to meet these parameters.

ATEX

V+ & V-

Input Voltage, U Input Current, I Input Power, P Input Capacitance, C Input Inductance, L

16.5V

340mA

1.3W

35nF

10µH

A & B

V+ & V-

Input Voltage, U Input Current, I Input Power, P Input Capacitance, C Input Inductance, L

11.8V

40mA

120mW

35nF

10µH

16.2V

317mA

1.28W

35nF

10µH

A & B

Input Voltage, U Input Current, I Input Power, P

Input Capacitance, C Input Inductance, L

11.8V

34mA

90mW

35nF

10µH

MFC010 Interface Manual

The output safety par ameters of t he bar rier dev ices m ust not ex ceed t he V oltage, P ower and C urrent limits set out above. T he output Capacitance parameter for the barrier devices must exceed the sum of the M FC010 i nput C apacitance, s pecified abov e, and t he m aximum c able Capacitance. The output Inductance par ameter f or t he bar rier dev ices m ust ex ceed t he sum of the MFC010 input Inductance, specified above, and maximum cable Inductance. To summarise:

Uo Barrier < U

Barrier < I

Barrier < P

Barrier > C

Barrier > L

MFC010

+ C

cable

MFC010

+ L

MFC010

NB The In-line resistance of the Modbus barrier MUST NOT EXCEED 1000 Ohms for each of the A and

B Input terminals.

The Z ener barrier devices must be i nstalled in an E MI s hielded enc losure and t he cable screen(s) kept intact right up to the barrier terminals as far as is practical. The cable screen(s) should be terminated to the enclosure, chassis Earth connection, and kept SEPARATE from t he i ntrinsically s afe E arth connections of the Barrier devices. The user MUST adhere to the barrier manufacturer’s instructions for connecting the intrinsically safe Earth connection to the barrier devices.

4.1 Power Supply Barrier Devices

The following Zener Barrier devices are those that are recommended for use on the V+ & V- power supply input connections to the MFC010.

Manufacturer : Bartec Part Number : 17-1834-1000/3715 Ex Approvals : EEx ia/ib IIC

Connection :

Manufacturer : Pepperl & Fuchs Part Number : Z765 Ex Approvals : EEx ia IIC FM and CSA Approved

Connection :

Note: For Optimass 2000 the supply voltage to the barrier should be +14V to ensure maximum voltage is supplied to the meter.

MFC010 Interface Manual

4.2 Modbus Barrier Devices

The following Zener Barrier devices are those that are recommended for use on the A & B Modbus input connections to t he M FC010. W hen s pecifying al ternate dev ices t he us er m ust ens ure t hat t he i n-line

resistance of t he M odbus bar rier DOES NOT EXCEED 1000 O hms f or eac h of t he A and B I nput terminals.

Manufacturer : Bartec Part Number : 17-1834-4000/0031 Ex Approvals : EEx ia/ib IIC

Connection :

Manufacturer : Pepperl & Fuchs Part Number : Z764 Ex Approvals : EEx ia IIC FM and CSA Approved

Connection :

4.3 Connection To The Modbus Bus

When installed in hazardous area application the MFC010 i nterface i s not di rectly c ompatible w ith t he Modbus interface standard due to the presence of the required Zener Barrier devices.

In a poi nt-to-point configuration, when the MFC010 is the only device on the bus, the cable length from the barriers to the “Master” host system must not exceed 10m in length. If a greater distance is required, the us e of a s uitable R S485 repeater is recommended, in which case the repeater connection to the Zener B arrier dev ices s hould not ex ceed 10m i n l ength. T he m aximum c able l ength bet ween t he Repeater and the “Master” host system is determined by the operating limits of those two devices. T he cable length from the Modbus barrier device to the MFC010 must be less than 300m i.e.

Where the distance from the barrier device to the MFC010 is less than 10m, two barrier devices may be connected in parallel to the “Master” host system, or the repeater if one is being used, refer to the diagram below. The overall cable length from the Host/repeater to the barrier devices must still be less than 10m as described previously. If more than two devices are required to be connected then a dedicated repeater should be used for each.

Each MFC010 MUST have its own dedicated barrier interface; they MUST NOT be connected in parallel on the hazardous area side of the system.

MFC010 Interface Manual

In a multidrop installation, see figure below, the Zener Barrier devices must be connected to the bus using a s uitable R S485 repeater, with the c onnecting c able bet ween the Barrier devices and t he repeater not exceeding 10m. The connection of the repeater to the Modbus bus must then follow the rules and restrictions of the Modbus protocol as indicated previously in section 3.4.

5. Modbus Protocol Interface

The interface to the MFC010 is implemented in the Modbus RTU communications pr otocol, and i s done so in accordance with the specification and requirements of the “Modbus Protocol Reference Guide” (PIMBUS-300 R ev J ). The phy sical el ectrical par ameters of t he M odbus s pecification are def ined by the EIA/TIA-485 (RS485) standard and t he “ Modbus ov er S erial Li ne - Specification and I mplementation Guide V1.0” interface definition.

In a serial communications system such as the Modbus protocol, data is transmitted as a series of voltage levels along the connecting data wires. A “bit”, or binary digit, value is determined by the logical level (high or low) of the connecting interface over a set time period. The time period for each bit is determined by the transmission speed, known as the baud rate. For a baud r ate of 9600, the bit period is 1/9600 =

104.2 m icroseconds. T he MFC010 supports Baud r ates of 1200, 2400, 4800, 9600, 19200, 38400 and

57600 baud (see the Baud rate setting in Holding Register No. 1005). The higher transmission speeds require careful attention to the cable installation in order to function reliably and error free (see Section 3.2 on page 7 for installation details).

5.1 Character Transmission Format

Data is transmitted in sets of 8 bit data blocks, known as “Bytes” or “Characters”. Each character i s preceded and followed by framing bits that permit the correct detection of the transmitted character. The first “Bit” transmitted will be the “Start” bit, this permits the receiving device to detect that a character is being transmitted. The “Start” bit is then followed by the 8-bit data byte. A “Parity” bit may then follow the 8-bit character. T his “Parity” bit is optional (see the Transmission format setting in Holding Register No.

1004), it allows the system to validate the c ontents of the 8-bit data byte to ensure that no er rors have

occurred during transmission. Following the “Parity” bit is the “Stop” bit that indicates the end of the transmitted character to the receiving device. If no parity bit is used, two stop bits must be implemented, this ensures a consistent character length of 11 bits is maintained.

The 8 dat a bits are annotated from bit 0 ( the least significant bit, LSB) to bi t 7 ( the most significant bit, MSB). The character is transmitted “MSB first”, i.e. the first bit after the start bit, is bit 7 of the data byte. See appendix B for more details on binary coding.

MFC010 Interface Manual

5.2 Modbus Telegram Format

The messages between the Modbus master and slave devices are transmitted as groups of characters, as des cribed abov e, c ollectively k nown as t elegrams. E ach t elegram i s preceded and followed by a “Quiet” period on t he Modbus bus of 3½ character periods. T he “Quiet” period following the telegram is used to indicate the end of the telegram.

The first character received in the telegram identifies the slave device to which or from which the telegram is bei ng t ransmitted. T his f irst c haracter i s k nown as t he S lave I D or S lave A ddress. In multidrop configurations (see Section 5.4 below) this address character is used by the master device to individually communicate with one of the instruments on the bus connection. T he Slave device returns this value to indicate to the master the source of the response telegram. The Slave Address value for the MFC010 can be set using Holding register No. 1006 (see Section 7.5).

The s econd character received in the telegram is the function command code r equested by the master device. A list of the function codes supported by the MFC010 can be f ound in Section 6 (See Page 23) along with a description of each.

The last two characters received form a 16 -bit checksum value. T his checksum value is used to ensure that t he dat a r eceived i n t he t elegram has not been c orrupted. T he c hecksum i s calculated and appended to the telegram by the transmitting device (Slave or Master) and the receiving device compares the received checksum value against the value it calculates from the received data. If the data has been corrupted in some way during transmission, then the checksum calculated by the receiving device will be different than that which it received with the telegram. The receiving device will then ignore the telegram knowing t hat t he dat a w ithin i s unr eliable. S ee A ppendix A for information on the Modbus Checksum calculation.

Between t he function code character and t he CRC checksum at the end of the telegram is the telegram data. The contents and format of these data characters is dependant upon the function code requested.

5.3 Data Types in Modbus

There are two data types used to transmit information on a Modbus data bus, the “Bit” and the “Register”. The “Bit” represents a s ingle binary state, whether as an output or an input condition. The “Register” is a 16-bit integer transmitted as two 8-bit c haracters. U sing multiple “ Registers” the Modbus interface c an transmit higher accuracy values such as “Floating Point” and “Double Precision Floating Point” numbers.

“Bit” variables are packed into 8 bit bytes, so each character sent or received can contain up t o 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 first indexed by the Master request address is transmitted in the LSB, Bit 0, of the first data character. T he next “Bit” value i s t ransmitted i n t he nex t bi t, B it 1, of t he f irst dat a c haracter. T his c ontinues until the last bit location, Bit 7, of the first data character is used. The next “Bit” value is then transmitted in the LSB, Bit 0, of the following data character, this continues until all of the requested values have been transmitted. Any unused bit locations in the last data character are filled out with “0”s

For simple single register variables the Most Significant Character of the register is transmitted first, with the Least Significant character following i mmediately after. H owever, f or variables that r equire m ultiple registers, i.e. the “Floating Point” and “Double Precision Floating Point” variables, the transmission order is a little more complicated. i.e.

Single 16 Bit Register Variables, Data Transmission Order

Byte 1, MS Byte Byte 0, LS Byte

Long Integer & Floating Point Variables, Data Transmission Order

Byte 1 Byte 0, LS Byte Byte 3, MS Byte Byte 2

Requested Register Requested Register + 1

Double Precision Floating Point Variables, Data Transmission Order

1 0 3 2 5 4 7 6

Requested Register Register + 1 Register + 2 Register + 3

5.4 Multidrop Operation

A “Master” dev ice, s uch as a P C or P LC, c an be us ed t o control and i nterrogate a num ber of “ Slave” devices, such as an MFC010, connected to the Modbus bus in a “Multidrop” configuration. The “Master” device always initiates the communication interchange with the “Slave” devices, each of which waits for instructions or requests from the “Master” before transmitting dat a on t he bus i n r esponse t o t he instruction. Although the Modbus specification allows for up to 247 “Slave” devices to be physically connected to the bus at any time, the Master device can only request information from one “Slave” device at a time. A unique ID number or “Address” is allocated to each of the “Slave” devices to allow the “Master” to differentiate between them. Although it does not matter in which order the “Slave” devices are interrogated, the “Master” must wait for the response, or for a suitable period after the request, before making a request to any other of the slave devices on the bus.

Under some limited conditions, i.e. when the instruction to the “Slave” device does not require a detailed response, the “Master” device can send a “Broadcast” command, indicated by a “Slave” ID Address of “0”, to all of the slave devices simultaneously.

5.5 Calculating Data Transmission Rates

Careful attention should be made to ensuring that the bus installation can support the amount and rate of data t ransmission r equired. C onsideration of t he l imitations of the physical installation, as previously described, s hould not be i gnored. T he m aximum us able t ransmission s peed, baud r ate, w ill depend entirely upon the installation.

The transmission format also needs to be carefully considered. In the Modbus standard, each transmitted character is 11 bi ts long, depending upon t he setting of the transmission f ormat. A t the Modbus default transmission speed of 19200 baud, each character will have a transmission period of 573 microseconds.

For a simple data transfer of one Input value (see section 6.4 on page 26 for details) between the master and slave will require an 8 character (+ 2 x 3½ character “Quiet” periods) telegram in the request from the master, and a 9 character (+ 2 x 3½ character “Quiet” periods) telegram in the response from the slave. If the Slave responds immediately the cycle from the Master sending the request to receiving the response will be at least 31 characters long, or 17.8 milliseconds at 19200 baud. T herefore the maximum rate of data requests that could be made is 56 every second.

In m ost c ases f ar m ore dat a w ill be required, and i n m ultidrop s ystems t he m aster dev ice m ay be requesting data from up to 64 units. In these circumstances the user must ensure that there is sufficient time i nterval bet ween r equests f or t he m easured v alues t o be received without overlapping the Master request telegram with the previous slave reply telegram.

To achieve the required update rates the user may have to consider whether, in a multidrop configuration, the number of devices on a bus must be l imited or whether the cable installation will support one of the higher data transmission speeds which are available.

This is especially important where fast response is required (such as batch filling operations).

MFC010 Interface Manual

5.6 Error Messages in Modbus

When t he M FC010 det ects an error i n t he r equest r eceived i n a pr operly f ormatted t elegram, i t w ill respond with an error message. The error message response telegram is formatted as follows.

Address Function Error Code CRC CRC

The most significant bit of the requested function code is set (add 128, 80

) in the response telegram to

indicate that an error has been detected. For example, if an error were detected in a Function 1 request, then the returned function code would be 81

(129).

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

1 Illegal Function The requested function code is not supported by the MFC010 or is not valid due to the current settings of the device.

2 Illegal Data Address The Register requested is not valid.

3 Illegal Data Value The requested data (in Write operations only) is invalid for the register being written.

6 Slave Device Busy The MFC010 is unable to process the requested

command because an EEPROM save is in progress.

Errors due t o c ommunications f aults ( CRC er rors, P arity er rors et c) ar e logged but no response is returned because the data in the received telegram is deemed unreliable. T he Master system can read the error logs by using the diagnostic command (Function 08, see Section 6.8).

6. Modbus Functions Supported by the MFC010

6.1 01 (0116): Read Coil Status

This f unction permits the user to read the state of a number of consecutive Discrete Outputs, or “Coil”, registers. Within the MFC010 the majority of the Discrete Outputs are used to initiate command functions; when read, response will be “ 1” w hilst c ommand i s bei ng processed and “ 0 when t he c ommand i s completed (See Section 7.2 on page 39 for details of the individual Status Output registers). The format of the Master request telegram for this function should be as follows.

Request Character

1 Slave Address 0116 Request to Slave ID 1

2 Function 0116 “Read Coil Status”

3 Start Address Hi 0316

4 Start Address Lo E916

5 No of Points Hi 0016

6 No of Point Lo 0516

7 CRC Lo 2D16

8 CRC Hi B916

The MFC010 will respond to such a request with a telegram formatted as follows.

Response Character

Field For Example

Start Address = 1002

No. of Points = 5

( “Coils” 1002 – 1006 )

CRC Checksum

Field For Example

1 Slave Address 0116 Response from Slave ID 1

2 Function 0116 “Read Coil Status”

3 Data Bytes in Response 0116 1 byte (5 States requested < 8 Bits)

4 Data Byte 1 1516 Data = 000101012

5 CRC Lo 9016

6 CRC Hi 4716

The number of data bytes in the response will depend upon the number of Discrete Outputs requested. The appropriate bit in each of the data bytes received will indicate each Discrete Output state requested. Therefore, each data byte in the response will contain a maximum of 8 Discrete Output “Coil” states. For example, if 19 Discrete Outputs are requested, then three data characters will be r eturned, with the first group of 8 out put states encoded in the first data byte, the second group of 8 out put states coded in the second data byte, and the last 3 output s tates coded in the first three bit locations of the last data byte. Bit 0 of the first response data byte will c orrespond t o t he “ Start A ddress” D iscrete O utput r egister specified by the request telegram. B it 0 of the second response data byte will correspond to the “Start Address” + 8 Discrete Output register and so on.

In the example above, 5 Discrete Outputs are r equested, s o onl y one dat a by te i s r equired i n t he response. The response data value shown above i ndicates t hat r egisters 1002, 1004 and 1006 ar e active, and that registers 1003 and 1005 are inactive.

CRC Checksum

MFC010 Interface Manual

6.2 02 (0216): Read Discrete Input

This function permits the user to read the state of a number of consecutive Discrete Input registers. (See Section 7.3, on page 41, for details of the individual registers). The format of the Master request telegram for this function should be as follows.

Request Character

1 Slave Address 0116 Request to Slave ID 1

2 Function 0216 “Read Discrete Input”

3 Start Address Hi 0316

4 Start Address Lo E816

5 No of Points Hi 0016

6 No of Point Lo 0C16

7 CRC Lo F816

8 CRC Hi 7F16

The MFC010 will respond to such a request with a telegram formatted as follows.

Response Character

Field For Example

Start Address = 1001

No. of Points = 12

( “Inputs” 1001 – 1011 )

CRC Checksum

Field For Example

1 Slave Address 0116 Response from Slave ID 1

2 Function 0216 “Read Discrete Input”

3 Data Bytes in Response 0216 2 bytes

4 Data Byte 1 CD16 Data = 110011012

5 Data Byte 2 0916 Data = 000010012

6 CRC Lo 2D16

7 CRC Hi 2E16

The num ber of dat a by tes i n t he r esponse will depend upon the number of Discrete Inputs requested. The appropriate bit in each of the data bytes received will indicate each Discrete Input state requested. Therefore, each data by te i n t he r esponse w ill c ontain a m aximum of 8 di screte i nput s tates. F or example, if 19 Discrete Inputs are requested, then three data characters will be returned, with the first group of 8 input states encoded in the first data byte, t he s econd gr oup of 8 i nput states c oded i n t he second data byte, and the last 3 input states coded in the first three bit locations of the last data byte. Bit 0 of the first response data byte will correspond to the “Start Address” Discrete Input register specified by the request telegram. B it 0 of the second response data byte will correspond to the “Start Address” + 8 Discrete Input register and so on.

In the example above, 12 Discrete Inputs are requested, so two data bytes are required in the response.

CRC Checksum

6.3 03 (0316): Read Holding Registers

This f unction per mits t he us er t o r ead t he v alue of a number of consecutive Holding registers. (See Section 7.5 on page 49 for details of the individual registers). The format of the Master request telegram for this function should be as follows.

Request Character

1 Slave Address 0116 Request to Slave ID 1

2 Function 0316 “Read Holding Registers”

3 Start Address Hi 0316

4 Start Address Lo FE16

5 No of Points Hi 0016

6 No of Point Lo 0316

7 CRC Lo 6416

8 CRC Hi 7F16

The MFC010 will respond to such a request with a telegram formatted as follows.

Response Character

Field For Example

Start Address = 1023

No. of Points = 3

( Input Registers 1023 – 1025 )

CRC Checksum

Field For Example

1 Slave Address 0116 Response from Slave ID 1

2 Function 0316 “Read Holding Registers”

3 Data Bytes in Response 0616 6 bytes ( 3 x 2 Byte Registers )

4 Data Byte 1 3F16

5 Data Byte 2 4916

6 Data Byte 3 0216

7 Data Byte 4 D416

8 Data Byte 5 F116

9 Data Byte 6 2216

10 CRC Lo 7D16

11 CRC Hi BD16

CRC Checksum

MFC010 Interface Manual

6.4 04 (0416): Read Input Registers

This function permits the user to read the value of a number of consecutive Input registers. (See Section

7.5 on page 493 for details of the individual registers). The format of the Master request telegram for this function should be as follows.

Request Character

1 Slave Address 0116 Request to Slave ID 1

2 Function 0416 “Read Input Registers”

3 Start Address Hi 0B16

4 Start Address Lo B816

5 No of Points Hi 0016

6 No of Point Lo 0216

7 CRC Lo F316

8 CRC Hi CA16

The MFC010 will respond to such a request with a telegram formatted as follows.

Response Character

Field For Example

Start Address = 3001

No. of Points = 2

( Input Registers 3001 – 3002 )

CRC Checksum

Field For Example

1 Slave Address 0116 Response from Slave ID 1

2 Function 0416 “Read Input Registers”

3 Data Bytes in Response 0416 4 bytes ( 2 x 2 Byte Registers )

4 Data Byte 1 9416

5 Data Byte 2 7B16

6 Data Byte 3 4216

7 Data Byte 4 9616

8 CRC Lo 1716

9 CRC Hi 6316

In t he ex ample abov e t he I nput r egister r equested c ontains a f loating poi nt num ber and needs to be accessed as a pai r of r egisters ( 3001/3002). T he r esulting 4 by tes i n t he dat a r esponse c an t hen be decoded into a floating-point number (See Section 5.3 on page 20 and Appendix C on page 93 for further details on encoding and decoding floating point numbers).

CRC Checksum

6.5 05 (0516): Force Single Coil

This function permits the user to set the state of a single Discrete Output “Coil” register. (See Section 7.2 on page 39 for det ails of t he i ndividual r egisters). I n t he M FC010 implementation, these registers are used t o i nitiate c ommands and functions. S etting t he O utput s tate i nitiates t he f unction, at tempting t o clear t he O utput s tate w ill r esult i n a dat a er ror. The format of the Master request telegram for this function should be as follows.

Request Character

1 Slave Address 0116 Request to Slave ID 1

2 Function 0516 “Force Single Coil”

3 Coil Address Hi 0316

4 Coil Address Lo E816

5 Force Data Hi FF16

6 Force Data Lo 0016

7 CRC Lo 0C16

8 CRC Hi 4A16

The MFC010 will respond to such a request with a telegram formatted as follows.

Response Character

Field For Example

Coil Address = 1001

Set Coil “Active”

CRC Checksum

Field For Example

1 Slave Address 0116 Response from Slave ID 1

2 Function 0516 “Force Single Coil”

3 Coil Address Hi 0316

4 Coil Address Lo E816

5 Force Data Hi FF16

6 Force Data Lo 0016

7 CRC Lo 0C16

8 CRC Hi 4A16

The MFC010 (slave) response telegram should be an exact duplicate of the master request telegram.

Coil Address = 1001

Set Coil “Active”

CRC Checksum

MFC010 Interface Manual

6.6 06 (0616): Preset Single Register

This function permits the user to set the value of a single Holding register. For this reason this command cannot be used to write to variables that occupy multiple consecutive registers such as floating point and long integer v ariables (See Section 7.5 on page 49 for details of the individual registers). The format of the Master request telegram for this function should be as follows.

Request Character

1 Slave Address 0116 Request to Slave ID 1

2 Function 0616 “Preset Single Register”

3 Register Address Hi 0316

4 Register Address Lo FB16

5 Preset Data Hi 0016

6 Preset Data Lo 2316

7 CRC Lo B916

8 CRC Hi A616

The MFC010 will respond to such a request with a telegram formatted as follows.

Response Character

Field For Example

Set Register 1020 = 35

CRC Checksum

Field For Example

1 Slave Address 0116 Response from Slave ID 1

2 Function 0616 “Preset Single Register”

3 Register Address Hi 0316

4 Register Address Lo FB16

5 Preset Data Hi 0016

6 Preset Data Lo 2316

7 CRC Lo B916

8 CRC Hi A616

The MFC010 (slave) response telegram should be an ex act dupl icate of t he m aster r equest

Set Register 1020 = 35

CRC Checksum

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