This list is does not claim to be academically correct. It is simply a way of explaining
the subject of measurement and control better. It is compiled in order of measure
or sense, inspect and control.
Typically a device that reacts to a physical property within its surrounds and provides
typically an electrical output. This output can be a switch, a solid-state signal,
an analogue output of sorts or a serial or bus type communication. Typically no display
A display is usually a device that accepts an electronic input from a sensor and
displays sensor output in a meaningful manner. It can usually scale, convert and
offset to reflect a particular unit .
A gauge is basically a combination of sensor and display.
The measurement of a physical property as provided by a sensor or gauge.
A sensor that has some sort of a set-point adjustment. It enables the device to signal
if the physical property being measured has reached a certain threshold level (limit)
or not. A simple process control method to switch something on or off when the threshold
Similar to the limit switch but used in conjunction with a gauge. The threshold value
is typically set on the display device and may be easily altered for different products
or process conditions. It is also provides the most simple form of control.
Nominal value /Set-point
The value that a physical property should maintain to achieve the optimal production
A continuous loop of measuring, comparison to set-point and issue of a control signal
to eliminate any deviation between the actual and the nominal.
Typically a control loop that controls a physical dimension that is not measured
on the final product. For example the temperature control of an extruder.
Quality Control A control-loop that involves measuring a physical aspect of the end-product
and adjusting the manufacturing device to maintain that physical aspect as close
to nominal as possible.
It is called on-line if the measurement and control takes place real-time and automatically
on the production line.
Due to cost of the equipment or physical restrictions only some aspects can be measured
or controlled on-line. Therefore most quality control is still performed off-line
in a manual or semi-automatic fashion.