The FAQ of

Machine Information Systems

This FAQ page will cover all aspects of the harware, software and electrical terminology used throughout this site. Although the wording here will more of a technical description rather than the lovely flowing explanation by example technique employed on the rest of the site.
BUT don't let that put you off looking at 'em.

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FAQ: What is a Machine Information System?
Essentially a machine or management information system is a data-gathering system displaying data at a remote viewing point, normally an existing Office PC. Data logging functions are more often than not also included as a matter of course. The system would allow a manager to sit at his/her desk and see the state of operation of all the machines connected into the system.
Additional for this FAQ see also:
Definition of Management Information System.
Introduction to Information Systems.

FAQ : What is a PLC?
You may want to read this on PLC's first, then just close the window afterwards.
The PLC, or Programmable Logic Controller, is a computer with a single mission in (it's) life. They are most commonly used in industrial applications, it usually lacks a monitor, keyboard, and a mouse, as it is normally programmed to operate a machine or system using but one program.

The machine or system user rarely, if ever, interacts directly with the PLC's program. When it is necessary to either edit or create the PLC program, a personal computer is usually (but not always) connected to it.

The PLC has a remarkable capacity for real-world I/O connectivity. Most PLC models feature a vast assortment of interchangeable I/O modules, which allow for convenient interfacing with virtually any kind of industrial or laboratory equipment.

Most PLCs are programmed in a special language called Ladder Logic. Ladder Logic is essentially a Boolean logic-solving program with a graphical user interface designed to look like an elementary wiring diagram, familiar to all industrial electricians.

There are several manufacturers of PLC's such as Mitsubishi, Siemens and ABB to name a few.
Additional for this FAQ see also:
The PLC.
The PLC Tutorial.

FAQ : What is a HMI?
This is a Siemens HMI panel, this particular model is a TD200. A HMI (also know as a MMI sometimes) stands for Human to Machine Interface and Man to Machine Interface respectively. Although MMI is not perceived to be politically correct these days so you will hear that term less and less.

The HMI's job it to convert the intentions and signals from a human into electrical signals for the machine information system to use. Thus in doing so, allows the human operator to make interactive changes in the software process and data. An example would be pressing a button to reset the production count.

HMI's quite often have a display incorporated into them as well to enable the operator to see the relevant data to the action being performed.

The evolution of the computer has and continues to have a great impact on society and industry. We are in an adjustment cycle with the current computer evolution, but more importantly some of us are trying to adjust to meet the changes for the coming decade.

Hardware and software are continually being enhanced. Computers are becoming more powerful and will eventually provide a far more effective man, sorry human to machine interface. But we're doing ok in the mean time!

FAQ : What is PID control?
PID can be described as a set of rules with which precise regulation of a closed-loop control system is obtained. Closed loop control means a method in which a real-time measurement of the process being controlled is constantly fed back to the controlling device to ensure that the value that is desired is, in fact, being realized.

The mission of the controlling device is to make the measured value, usually known as the PROCESS VARIABLE, equal to the desired value, usually known as the SET POINT. The very best way of accomplishing this task is with the use of the control algorithm we know as PID.

In its basic form, PID involves three mathematical control functions working together: Proportional-Integral-Derivative. The most important of these, Proportional Control, determines the magnitude of the difference between the SET POINT and the PROCESS VARIABLE (known as ERROR).

This then applies appropriate proportional changes to the CONTROL VARIABLE to eliminate ERROR. Many control systems will, in fact, work quite well with only Proportional Control. Integral Control examines the offset of SET POINT and the PROCESS VARIABLE over time and corrects it when and if necessary.

Derivative Control monitors the rate of change of the PROCESS VARIABLE and consequently makes changes to the OUTPUT VARIABLE to accommodate unusual changes.

Each of the three control functions is governed by a user-defined parameter. These parameters vary immensely from one control system to another, and, as such, need to be adjusted to optimize the precision of control.

The process of determining the values of these parameters is known as PID Tuning.

PID Tuning, although considered "black magic" by many, really is, of course, always a well-defined technical process. There are several different methods of PID Tuning available, any of which will tune any system. Certain PID Tuning methods require more equipment than others, but usually result in more accurate results with less effort.

FAQ : What is a Diode?
A Diode is an electronic component, it can be thought of as an electronic valve. It serves one purpose in that it will allow a signal one way though it, but will block a signal passing through the other way. It is made up of 'P' and 'N' semiconductor material, these are etched on a substrate which is an insulator and also helps to attach wires. This whole little package is then encapsulated in a glass or plastic bead. Many different uses can be gained from its blocking function depending on the signal presented to the diode and its method of connection within other supporting components.

FAQ : What is a LED?
L.E.D. Stands for light emmiting diode. A light-emitting diode (LED) is very similar electrically to the diode above, with the one exception.
The LED will emit incoherent narrow-spectrum light when electrically biased in the forward direction of the P-N junction. (WHAT!!)
When a voltage is correctly applied to a LED, it is called being forward biased (conducting the current). P and N are the semiconductor materials diodes and transistors are made up of.
This lighting effect is a form of electro luminescence. The colour of the light emitted from the LED depends on the composition and condition of the semi conducting material used in its construction. The range of colour can be infrared light, visible light in a wide variety of colours or near-ultraviolet.

FAQ : What is a Transistor?
Generally speaking, a transistor is an electronic switch, it switches electrical signals (and power) one way, from positive to negative (NPN) or negative to positive (PNP). You could think of it like the little ol' diode above with an on/off button. Transistor are more commonly used as amplifiers of smaller signals and they are the fundamental building block component in the control circuits of most electrical equipment like computers, televisions and mobile phones etc. Transistors are made up of 'P' and 'N' semiconductor material in a slightly different manor to the diode, transistors are referred to as either PNP or NPN types. This defines which direction a transistor will switch a signal voltage.

They are so named because of the arrangement of semiconductor material they are made up of. They have three connections or legs as they are called, a collector, a base and an emitter. The switch is made between the collector and emitter, using the base as the on/off signal.

An NPN transistor will switch a positive voltage on the collector to the emitter, if a positive voltage is placed on the base with respect to emitter.
A PNP transistor will switch a negative voltage on the collector to the emitter, if a negative voltage a placed on the base with respect to emitter.

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