The more traditional types of controls can, of course, also be used for computerised systems. Controls that have been produced specifically for communicating with computers include:
1. Keyboard with predetermined functions for various keys
2. Keyboard with variable functions for the keys
3. Light pens
4. Touch screen
5. Electronic data board
6. Voice identification
7. Trackball and joystick (multiposition lever)
5.5.1 Keyboards with Predetermined Functions for the Keys
Keyboards with predetermined functions for all keys normally have two main parts: an alphanumeric or a numeric part and a function key part. The traditional keyboard—numeric or alphanumeric—will be discussed later. The function key part has different keys for different predetermined tasks, such as starting, stopping, process a, b, c, and so forth. The keyboard works by the operator pressing the keys in a certain order. The operator either remembers the order or uses some form of crib – sheet. The sequence in which the keys are to be pressed is thus often predetermined both by the system and by the design of the keyboard.
This type of keyboard is characterised by the need for a large number of keys, usually one per function. Where there are many functions and several subfunctions within every main function, problems arise with grouping the keys in the proper way and in positioning the keys in a mutually logical way that is consistent in terms of movements. It is unusual to be successful with this at the first attempt; the keyboard will need to be redesigned when it has been operational for long enough to build up enough experience to determine its optimal design. Making changes to the keyboard is often costly, but if the keyboard is not redesigned at a later stage, it means that large and frequent arm movements become tiresome, time consuming, and sometimes painful. The advantage of this type of keyboard is that it needs relatively little computer programming and, to a certain extent, a standard board can be used with minimal training, at least for the alphanumeric part.
The alternative to having a large number of function keys is to have just a few of them, and to use particular codes instead that can be entered numerically or alphanumerically. This type of keyboard is best when the operator is spending a large part of his or her working time at the keyboard. However, this is relatively uncommon in process industries.