Using the KD485 with Eurotherm / Schneider Electric Controllers

The KD485-ADE can be used to interface to Eurotherm / Schneider Electric controllers as a replacement for Eurotherm 241 / D241 and Eurotherm 261 / D261 interface converters (providing RS232 to RS422 conversion).

The KD485-ADE-4XX-4XX can be used to replace the Eurotherm D261 interface converter (used for 4 wire RS422 to 2 wire RS485 conversion).

The following information describes the required connections for a variety of Eurotherm instruments.

Series 2000

Communications to this series uses RS485, 2-wire mode. On the KD485-ADE Port 2 connect:

1 Terminals TXA and RXA
2 Terminals TXB and RXB

The above places the KD485-ADE RS485 port into a 2-wire mode.

To connect to the instrument(s) connect:

3 TXA+RXA to HE
4 TXB+RXB to HF
5 GND to HD

818, 815. 808, all 900 series units, Slave communications only

These instruments all use 4-wire RS485 mode. The connections required are shown in the following table.
Note that the terminal labelling varies between different instrument types and the table reflects this.

* Note 1: If there are several instruments connected to the line they must be wired as a single point-to-point link (i.e. without any spur connections). A 100ohm resistor should be connected across the RX+ and RX terminals of the instrument which is at the opposite end of the link from the KD485.

* Note 2: The COM link is usually not required. In cases where significant interference with the communications is encountered, the use of this link may reduce the problem. The wire used for this link should be carried within the screening of the communications cable. The screen should not be used for this purpose.

PC3000

In order to connect between an LCM or ICM port and the KD485 the D-type connector will have to be removed from the cable supplied by Eurotherm and the wires connected directly to the terminals of the KD485. If Standard Eurotherm cables are not used for this purpose then the special connector will have to be obtained from BERG. It is recommended that a standard cable is modified.

* Note 3: A terminating resistor should be fitted across these terminals. Dependent on the port and module it may be necessary to fit a PCB mounted link to achieve this. Please refer to the PC3000 documentation.

Other Instrument Types

Refer to the table for the 818, Using the "Function in Instrument" column, identify the terminal with the equivalent functionality on the instrument to be connected, Connect accordingly, There are some generally applicable rules and exceptions to this:

Equipment which follows the above rule:

• Eurotherm Drives
• Eurotherm Thyristor Stacks
• Eurotherm Process Automation Controllers

Equipment which does not follow the above rule:

• Chessell Recorders

For these instrument types you should invert the polarity of both the RX and TX channels, i,e, if the instrument terminal is labelled "TX+" you should wire it as if it were called "TX-" and connect it to terminal RXB on the KD485, Please remember that it is not possible, using the standard KD485, to mix instruments which use 4-wire communications on the same link as instruments which use 2-wire communications, even if they are using the same communications protocol.

Wiring 2-wire RS485

To use an RS485 instrument with a PC, buffer the RS232 port of the PC using a KD485-ADE as a RS232 to RS485 converter. Eurotherm does not recommend the use of a RS485 board built into the computer since this board is unlikely to be isolated, whih may cause noise problems and the Rx terminals are unlikely to be biased correctly for this application.   

To construct a cable for RS485 operation, use a screened cable with one (RS485) twisted pair plus a separate core for common. A common or screen connection is recommended as it will significantly improve noise immunity.

Wiring RS422 and RS485 Controllers

It is generally not possible to connect controllers using a 2-wire standard to controllers on a 4-wire standard. This may be required, for example, if 2000 Series controllers are to be added to an existing installation. 

It is, however, possible to modify the existing communications link by adding a special version of the KD485 converter unit (KD485-ADE-4XX-4XX). This is shown in the diagram below.

The first KD485-ADE unit below is the standard RS232 to RS422 (or RS485) type. It convert from RS232 to 4-wire RS485 and this link is used to communicate to the existing Eurotherm controllers. The second KD485-ADE is the special KD485-ADE-4XX-4XX version which converts from 4-wire to 2-wire RS485 communications. Its input side behaves to the 4-wire link as another controller would on an existing system, whilst at the same time, the communications messages from the computer are passed on to the output side of this unit. This is connected to the 2-wire communications link that will contain the series 2000 controllers. Any responses from controllers on this link will cause data to be placed on to the 4-wire link and then will be passed back to the computer.