Search results
Results from the WOW.Com Content Network
Loop-powered "I to P" (current to pressure) converters can convert the 4–20 mA signal to a 3–15 psi pneumatic output for control valves, allowing easy integration of 4–20 mA signals into existing pneumatic plant. Field instrumentation measurements include pressure, temperature, level, flow, pH or other process variables.
The second type of positioner is an analog I/P positioner. Most modern processing units use a 4 to 20 mA DC signal to modulate the control valves. This introduces electronics into the positioner design and requires that the positioner convert the electronic current signal into a pneumatic pressure signal (current-to-pneumatic or I/P).
The processors receive information from input modules, process the information and decide control actions to be signalled by the output modules. The field inputs and outputs can be analog signals e.g. 4–20 mA DC current loop or two-state signals that switch either "on" or "off", such as relay contacts or a semiconductor switch.
A digital current loop uses the absence of current for high (space or break), and the presence of current in the loop for low (mark). [1] This is done to ensure that on normal conditions there is always current flowing and in the event of a line being cut the flow stops indefinitely, immediately raising the alarm of the event usually as the heavy noise of the teleprinter not being synchronized ...
Showing the evolution of analog control loop signaling from the pneumatic to the electronic eras Current loops used for sensing and control signals. A modern electronic "smart" valve positioner is shown, which will incorporate its own PID controller.
Get AOL Mail for FREE! Manage your email like never before with travel, photo & document views. Personalize your inbox with themes & tabs. You've Got Mail!
A control loop using a discrete controller. Field signals are flow rate measurement from the sensor, and control output to the valve. A valve positioner ensures correct valve operation. The simplest control systems are based around small discrete controllers with a single control loop each. These are usually panel mounted which allows direct ...
Switch enclosures may also be required to be weatherproof, corrosion resistant, or submersible. An electronic pressure switch incorporates some variety of pressure transducer (strain gauge, capacitive element, or other) and an internal circuit to compare the measured pressure to a set point. Such devices may provide improved repeatability ...