Weighing indicator connexion's with PLC and PC Computer
In the field of industrial weighing we are usually connecting two types of computers to process weight information:
» PLC (Programmed Logic Controller)
In industry PLC is used to control or automate production lines.
The main difference between computers and PLCs is that PLCs are designed for severe conditions such as dust, moisture, heat, cold, etc. They also easily control input/output (I/O). These input/output connect PLC to sensors and actuators which read limit switches, variables analog process (such as weight) and positions of complex positioning systems. With actuators PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs.
» PC Computer
PC computers today are mainly based on Intel/Windows architecture.
They are used as standalone work station or connected on Ethernet Network.
In industry they are also used to make data acquisition and supervision and can be connected to weighing instruments.
Which connection to choose?
Basic history
One of the first advantages of weighing electronic systems is to be able to handle easily real-time weight information.
The first weighing electronic device was transmitting weigh information in the form of a 0 to 10 volts tension or in the form of 4 to 20 milliamps current.
0V or 4mA value is equal to 0 kg and 10V or 20mA represent the instrument maximum weight. These types of communication are called “analog output”. These systems were intensely used from 1965 till 1975.
Then, came the parallel digital communication era. The communication format was “binary coded decimal” code (BCD) with 4 digits in parallel. Main advantage of BCD is accuracy.
In the 80s, data serial communication came with the microprocessor era and the first true standard of communication "Modbus".
Then in 90s came the first field buses which are superhighways for the industrial automatisms.
Since 2000, choosing a connection became more and more complex due to a lot of new technologies and the necessity to keep communicating with old systems always in use.
As a great specialist in communication ARPEGE MASTER K got well known in 1987 with the release of its IDM weight indicator. Through the MINITEL (old French modem terminal) the IDM was connected via the
telephone network and could be calibrated at distance. The IDM was the first "web server" indicator.
Now all ARPEGE MASTER K indicators can be at least connected to a computers PC by its serial Com1 port and our ERIC (Emission/Reception/Indicator/Computer) protocol just send a letter from the computer
such as "P" to get the indicator weight value.
Note: protocol is the word used to define methods used to exchange data between 2 machines.
Arpège Master K solutions
The most communicating indicator is the IDé 100 which has in standard 2 serial ports, one printer parallel port and it support several protocols:
- 0/10 volts or 4/20 mA isolated accuracy output (option boards) with PLC,
- Serial communication protocol (on RS 232 or RS 485 support): Modbus with PLC,
- USB slave protocol compatible with common PC,
- PLC field buses (with option board):
- Profibus DP compatible with Siemens and Hitachi PLC,
- Device Net compatible with Allen Bradley and Omron PLC,
- Modbus on Ethernet called Modbus TCP compatible with Schneider PLC,
- Interbus S developped by Phoenix Contact and can be used with Schneider PLC.
The Magic indicator is a process oriented weight indicator that supports PLC connection with: option board 0/10 v and 4/20 mA output, Modbus RS485, Profibus DP and Ethernet Modbus TCP.
With Can-Dy EX transmitters, the multichannel indicator
IDé 500-I is able to manage up to 12 ways of measure at the speed of 100 measures by second.
It supports the same field bus options than the above IDE 100. The IDE 500 I is the PLC ideal companion.
