To make physical objects move from a web browser on your smart phone or computer from anywhere may sound simple. However it is a mesh of intermingled systems and disciplines. To make systems rugged, reliable, safe, secure and up-gradable can be somewhat of a challenge. There is no plug and play solution which suits every environment.
If your machinery does not need smart phone control and only has:
- a few on / off routines,
- some logical sequences
- mixed in with timed or calendared events
then maybe a programmable relay will do the job as it simplifies complex wiring.
It can start large industrial motors and have sensors attached.
If the situation requires more features then the step is made to a PLC.
PLC – Programmable Logic Controller
A PLC is a type of computer which does not have a desktop interface like most of us are familiar with. Unlike a normal computer it has points you can connect wires to known as I/O (input and Output). The I/O allows the PLC to interact with the real world. They can move small objects the size of a match box all the way through to the engine in an 80,000 tonne ocean going ship.
The I/O wires only handle and supply small amounts of power. Thus an interface is needed to step up the output power for the machinery or filter down the signal to the PLC inputs. To create these interfaces an electrical engineering skill set is required.
When the number of machines to control becomes impractical for one PLC, or data is to be collected we step to a DCS or SCADA system.
DCS and SCADA
DCS (Distributed Control Systems) are usually an array of PLCs which control various sections of an operation. Thus if one section of the operation has to stop, the other can keep going. They all communicate and work together. The array of PLCs could adapt to the link in the chain which is not working.
SCADA (Supervisory Control And Data Acquisition) is usually a central computer which over sees a DCS array of PLC’s. It is somewhat of a grey area now as to whether a system is strictly DCS or SCADA. However the central computer is often assigned the task of collecting data into a database.
For potentially dangerous environments we install separate safety systems which can shut down the main system, but still communicate with the overall system.
For mission critical systems where downtime is unacceptable and must be minimized, redundant cabling and redundant PLCs are implemented.
Smart phone control
Once there is a database involved, scripts can be embedded in traditional style web pages to give control to the end user. There are also options to see an image of touch screens attached to PLC’s.
The smart phone web layout is roughly based on the HMI (Human Machine Interface). Except it is greatly cut down only showing some key elements which may be needed from remote locations.
An example of a smart phone HMI can be found here.
IOT – Internet Of Things
in a nutshell, we now have options to send information to and from the control system using low bandwidth connections. Small stand alone sensors and controllers are becoming more readily available. For example we may want to open a gate kilometres away and the operation of this gate may benefit the overall control system at the main factory. There are now possibilities to use modern stand alone smart devices to connect back to the main factory. These smart devices don’t quite fit any existing genre, thus the IOT genre has evolved.
New low power / low data rate wireless connection modules can now be attached to devices with ranges up to 10km. Control or data collection from simple machines far away often only needs to happen once an hour, or once per day. Thus these wireless IOT devices can be a solution.