Instrumentation & Sensors
Flow meters are devices that measure the flow rate of a liquid or a gas as it passes through a pipe. They can measure everything from temperature, density, pressure, vapor pressure and viscosity. Flow meters can also be used to monitor safety conditions.
Level switches are devices that are used to monitor the level of a substance within a system, usually a reservoir or a tank. When the substance is outside of the set parameters (low or high), the switch can trigger an alarm to signal the system to modify the level (open a valve or start a pump).
Pressure sensors are devices that measure the pressure in liquids or gases and then, based on that information, will generate an electronic signal.
Pressure transmitters are devices that can measure pressure ranges in liquids or gases. The value is then transmitted as an electronic signal.
Light curtains can be used instead of a solid guard to protect personnel around hazardous machines. The light curtain uses presence detection between a transmitter and a receiver. When a presence is detected, a signal would be sent to turn off the machine to prevent injury.
Limit switches are electromechanical devices that detect the presence or absence of an object or to detect when the movement limits of an object have been exceeded.
Photoelectric sensors emit a beam of infrared or visible light that is used to detect whether an object is present or absent, or whether there are changes in surface conditions. When the light is interrupted or reflected by the object, the change in the amount of light arrives at the receiver. The receiver converts the change to an electrical output signal.
Subcategories
Digital signals are represented in either a true or false. There is no gray area with digital signals. An example of this might be a light switch. A light switch is either on or off. Another example of this might be a motor that is running or not running. Digital signals can be generated with both AC and DC circuits with varying voltages, currents and resistance. Some practical examples of using digital signals in an industrial environment might be if a pump is running or not running or a whether a valve is open or closed.
Analog signals convey information in the form of a range. A light switch might be on or off as a digital signal, but a dimmer switch would be an analog signal. It can be on or off, but it can also be somewhere in between. A practical example of using analog signals in an industrial environment would be if there is a need to measure the level of a tank; whether it's full, empty or somewhere in between. Analog signals can take many different forms with some of the more common being a 4 to 20 milliamp signal or a 0 to 5 or 0 to 10 volt signal.
Communication in a device can either be sent or received. Whether that data is sent or received depends on the type of information. Is there a need to monitor the status of something? If so, an input needs to be received about that information. Is there a need to control something? If so, an output needs to be sent about what needs to occur. Receiving inputs and setting outputs are both things that can be accomplished by using both digital and analog signal types. Therefore, the signals are referred to as analog outputs (AO), analog inputs (AI), digital inputs (DI) or digital outputs (DO).