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IFC 100
IMPORTANT INFORMATION 1
The flow converter with the RS485 interface card fitted, is able to communicate with an external
device (PC or other suitable computer system) using the Modbus protocol. This option allows
data exchange between PC or computer and single or multiple devices.
The bus configuration consists of one external device as a master and one or more converters as
slaves. For bus operation the device address (menu C5.8.1), baudrate (menu C5.8.2) and settings
(menu C5.8.3, C5.8.4, C5.8.5 & C5.8.6) must be set in the converter.
All devices connected to the bus, must have different unique addresses but the same baud rate
and settings.
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ProtocolModbus RTU (available as a separate document on request)
Maximum participants on bus32 per line, master included (may be extended by repeaters)
CodingNRZ bit coding
Address rangeModbus: 1...247
Transmission procedureHalf duplex, asynchronous
Bus accessMaster / slave
CableShielded twisted pair for RS 485 applications
DistancesMaximum 1.2 km / 3937 ft without repeater (dependant on
baud rate and cable specifications)
2.2 Technical data of the Modbus interface (acc. to EIA standards)
Kind of signal transmissionDifferential, 2-wire topology
Maximum number of
transmitter/receivers
Voltage range on converter input-7...+12 V
Maximum voltage on converter output5V
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
(refer to chapter "Electrical connection")
32
U
>1.5V
diff
120 Ω / 560 Ω
IFC 100
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IFC 100
CONNECTION IN BUS SYSTEMS 3
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, normally the "end".
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4 LOCAL CONFIGURATION
IFC 100
Converter Fct.
DisplayDescription and settings
No.
C5.8.1Slave AddressSelects the Modbus address of the device.
C5.8.2Baud RateSelects the baud rate of the device.
C5.8.3ParitySelects the parity.
C5.8.4Data FormatSelects the data format.
C5.8.5Transmission DelaySelects the delay between receiving the last byte of a request and
C5.8.6Stop BitsSelects the number of stop bits.
C5.8.7InformationDisplays information about the device.
sending the first byte of the response.
Range: 0..40ms (default = 0ms)
Options:
1 (default) / 2
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IFC 100
ELECTRICAL CONNECTION 5
Refer to the standard handbook of the converter for connection details.
Modbus connections
TerminalsDescription
B-Signal B (D 1)
BSignal A (D 0)
C-Common 0 V
C3.3 V; 560 Ω
D-Pulse output -
DPulse output +
Example for bus termination
R1: 120 Ω
R2: 560 Ω
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6 MODBUS PROTOCOL
6.1 General information concerning the protocol
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.
Synchronisation 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.
6.2 RTU frame format
The format of the query and response frames vary slightly depending upon the command
function. The basic form is outlined below.
Command functionFrame formatDescription
IFC 100
Silent period3.5 x TAll transmissions must be preceded by a minimum silent
Slave address8bitsThis is a single byte slave address which is transmitted
Function code8bitsThis is an eight bit code in the range of 1...255 although
Register start address or
byte count when required
Number of points or data
bytes when required
8 bit byte count
16 bit address
n×8bitsNumber 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. at 19.2 kb no parity with 1 stop bit (10 bits),
T=520µs.
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: for a query command that requires
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 30006dec = 7536hex.
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).
CRC16 bitsThis field contains a 16 bit CRC which is calculated on all
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the data bits of the message bytes.
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IFC 100
6.3 Addressing
In the following tables the Modbus protocol addresses / data addresses are listed.
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;
• for Input Registers replace the leading 20 of 20xxx by 9xxx.
MODBUS PROTOCOL 6
Sometimes register numbers are asked for. The register numbers
register numbers can be calculated by adding a
register numbersregister numbers
1 to the protocol address and using a prefix according to the block:
• prefix 1 for coils
• prefix 3 for Input Registers
• prefix 4 for Holding Registers
6.4 Overview of supported functions
The following table shows Modbus functions supported by RS485 interface.
Function codeNameAccess to
hexdec
0101Read Single CoilStatus of calibration functions, counter
0303Read Holding RegisterAcyclic Registers
0404Read Input RegisterCyclic Register
0505Write Single CoilCold start, warm start, error reset, start
Measurement values, status values and
calibration results
calibration function, start/stop counter
Signal converter configuration parameter
Identification
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6 MODBUS PROTOCOL
IFC 100
6.5 Device identification on the Modbus interface
The device identification is according to the category "Regular" according to the Modbus
Application Protocol Specification V1.1a. Function code 43 / 14 (0x2B / 0x0E).
Modbus object IdObject name / DescriptionTypeContent
0x00VendorName16 byte ASCII StringKROHNE
0x01ProductCode10 byte ASCII StringCG number; order code for the
0x02MajorMinorRevision7 byte ASCII StringV1.0.xx
0x03Vendor URL32 byte ASCII Stringwww.krohne.com
0x04ProductName16 byte ASCII StringIFC100
0x05ModelName16 byte ASCII StringModbus
0x06UserApplicationName16 byte ASCII StringUser tag, displayed on the
converter assembly
header of the local screen
6.6 Coil registers
These function codes are used for access:
• 0x01 = read input coil
• 0x05 = write single coil
6.6.1 Converter controls
Coil addressFunction
1000Write 1 generates a cold start, write 0 is ignored
1001Write 1 generates a warm start, write 0 is ignored
1002Write 1 generates an error reset, write 0 is ignored
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IFC 100
6.6.2 Counter controls
MODBUS PROTOCOL 6
Modbus protocol
DescriptionSettingsConverter Fct. No.
address
3000Start / Stop
Counter 1
3001Start / Stop
Counter 2
3002no function
3003Reset Counter 1Write1reset counterC3.1.6
3004Reset Counter 2Write1reset counterC3.2.6
3005no function
Write1start counterC3.1.8 / C3.1.9
Write0stop counter
Read1counter is running
Read0counter is stopped
Write1start counterC3.2.8 / C3.2.9
Write0stop counter
Read1counter is running
Read0counter is stopped
Write0-
Read0-
Write0-
Read0-
6.6.3 Start calibration functions
Modbus protocol
DescriptionSettingsConverter Fct. No.
address
2000Zero CalibrationWrite1start functionC1.1.1
Write0-
Read0-
2001Coil Temperature
Calibration
2002Electrode Factor
Calibration
Write1start functionC1.1.8
Write0-
Read0-
Write1start functionC1.1.11
Write0-
Read0-
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6 MODBUS PROTOCOL
6.7 Input registers
All input registers in the Modbus protocol address range from 30000 to 38998 are mapped into
the range 0 to 8998. All input registers in the Modbus protocol address range from 20000 to
20998 are mapped into the range 9000 to 9998. This is done to give systems with restriction on
the address range access to the device.
Measurement and status values are read only and can be accessed as Modbus "Input Registers".
Cyclic GDC objects are mapped to Modbus Registers.
Function code is 04 (0x04).
IFC 100
Modbus protocol
Description and settingsTypeNumber of registers
address
1st2nd
300000flow speed
300022
300044mass flow
300066coil temperature
300088conductivity
3001010diagnosis value
3001212Display Channel 1
3001414Display Channel 2
3001616Operating time
3001818Not used, returns zerofloat2
3002020
3002424
3002828Not used, returns zerodouble float4
3003232long status sensor
3003434long status device
flow speed [m/s]float2
flow speedflow speed
volume flow
volume flow [m3/s]
volume flowvolume flow
mass flow [kg/s]float2
mass flowmass flow
coil temperature [K]float2
coil temperaturecoil temperature
conductivity [S/m]
conductivityconductivity
This value may not be measured.
Depending on register (4)2003.
0 = off (not measured)
1 = conductivity [S/m]
2 = cond. + empty pipe (S) [S/m]
3 = cond. + empty pipe (F) [S/m]
4 = cond. + empty pipe (I) [S/m]
diagnosis value
diagnosis valuediagnosis value
This value may not be measured.
Depending on register (4)2011.
25 = off (not measured)
31 = electrode noise [m/s]
8 = terminal 2 DC [Volt]
9 = terminal 3 DC [Volt]
Display Channel 1
Display Channel 1Display Channel 1
Represents the value on the first line of
the first measurement screen in SI units
Display Channel 2
Display Channel 2Display Channel 2
Represents the value on the first line of
the second measurement screen in SI
units
Operating time [s]float2
Operating timeOperating time
Counter 1
Counter 1 [m3] or [kg]
Counter 1Counter 1
Counter 2
Counter 2 [m3] or [kg]
Counter 2Counter 2
long status sensorbyte [4]2
long status sensorlong status sensor
long status devicebyte [4]2
long status devicelong status device
float2
float2
float2
float2
float2
double float4
double float4
12
Input register 30018 is not used up to now. This is included to fill the gap between the float and
double float values and allows to read the full range of registers.
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IFC 100
MODBUS PROTOCOL 6
Also the result of a calibration procedure is accessed by an input register at Modbus Protocol
Address 20000 or 9000. The type are one or more float values. This is depending on the used
function (refer to "Calibration procedures").
Modbus protocol
Description and settingsTypeNumber of registers
address
1st2nd
200009000Result of a calibration functionone or more float
values
6.8 Holding registers
All holding registers in the Modbus protocol address range from 40000 to 49998 are mapped into
the range 0 to 9998. This is done to give systems with restriction on the address range access to
the device.
Some parameters of the device can be accessed as Modbus "holding registers".
Function code 03 (0x03) for "Read" operations and function code 16 (0x10) for "Write" operations.
The holding registers are grouped into the following different sections.