{{unreferenced, date=November 2008
Digital
Digital usually refers to something using discrete digits, often binary digits.
Technology and computing Hardware
*Digital electronics, electronic circuits which operate using digital signals
**Digital camera, which captures and stores digital i ...
test
Test(s), testing, or TEST may refer to:
* Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities
Arts and entertainment
* ''Test'' (2013 film), an American film
* ''Test'' (2014 film), ...
controllers are devices (usually
computer
A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
based) that provide
motion control
Motion control is a sub-field of automation, encompassing the systems or sub-systems involved in moving parts of machines in a controlled manner. Motion control systems are extensively used in a variety of fields for automation purposes, includi ...
by processing digital signals. Typically a controller has inputs connected to
sensors
A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon.
In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
on the device they control, which measure the
feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
, its current state (for example the current position), and process this signal to provide an output to a hydraulical, electrical or other type of
servomechanism
In control engineering a servomechanism, usually shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. On displacement-controlled applications, it usually includes a built-in ...
control of the controlled device, with the aim of matching a control signal.
A good example is an
elevator
An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...
. The control signal is the button selects the floor the passenger wants to go. The controller of the elevator looks at which floor the elevator currently is (current position), at the floor selected (by the button) and by comparing them to each other derives a signal to control a servo (either hydraulic or electric) that makes the elevator move until the right floor is reached.
In the older days test controllers were usually analog, but with the rapid developments in
digital signal processing
Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
and computer technology, test controllers are almost exclusively digital devices. This offers many advantages, because it allows the user to execute all kinds of additional operations on the digital signals, in addition to the standard
PID controller
A proportional–integral–derivative controller (PID controller or three-term controller) is a control loop mechanism employing feedback that is widely used in industrial control systems and a variety of other applications requiring continuou ...
. Digital test controllers offered by
Moog, provide novel advantages for this type of system control.
Image:Digital Servo Controller.jpg, A modern digital test controller
Control devices