Controllers in detail

Controllers are the heart of the sensor to boardroom integration scenario. Controllers are basically a microprocessors. The processing capability of these microprocessors vary based on the application. For example, if you take the case of Flow controllers or Batch controllers the microprocessor is capable of process two letter commands and maximum of less than 100 commands. The configuration parameters will be stored in PROM type memory (no hard disk). There will be an Input / Output (I/O) circuit board. Using the I/O board users can connect digital or analog input and output devices. The input devices in this case are solenoid valve, flow measurement devices like Positive Displacement (PD) meter, valve position sensor. The output devices are display units, printers.

The controllers can be communicated through a personal computer connected to it. The communication takes place using serial mode (RS - 232/ 422/ 485). The communication protocol plays a major role in establishing connection. Most of the controllers developed earlier days had a proprietory protocols (e.g. smith protocol in AccuLoad controllers). Recent developments in the industry forced the controller vendors to standardise with MODBUS protocol. This will be the standard for controller communication, in the near future.

Also, recent influence of Information Technology (IT) developments added TCP/IP mode of data transmission in the Industrial Automation network as well. The controllers research and development initiative progressed in the following mode of communication :
1. Modbus protocol support
2. TCP/IP
Today's advaced controllers are provided with Modbus communication port and TCP/IP port apart from traditional RS-232/422/ 485 ports.

Hence, if you are interested in connecting a set of similar devices to Manufacturing Execution System (MES) or directly to ERP and other systems, best bet would be to have Serial to TCP/IP converters. Integrate the sensors to the controllers using serial mode and controllers to the external system using TCP/IP mode. These serial to TCPIP converters are provided with optional output USB Port and Fibre Optic cable port. Fibre Optic cable port can be used if the controller need to be located in a remote place and far from the communicating computer.

Also, the remote controllers can be connected to the TCP/IP converter which in turn can be connected to a wireless LAN device and an in-built GPRS enabled device. This helps in trouble shooting of controllers situated in remote locations e.g. Remote Terminal Units (RTU) in the cross country pipelines of Oil & Gas industries.

More information below,
Controller : Batch controllers http://www.ryanhercoflowsolutions.com/Markets/VendorArticles/Signet/BatchControls.pdf
Modbus protocol : http://www.modbus.org/docs/PI_MBUS_300.pdf
Serial-to-TCPIP converters : http://www.moxa.com/product/NPort_S8000.htm