I think I have that right. I have a device that has '4-20 mA' printed on it. Should I read that as meaning the device is 0.4amps?
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no.... 0.4 amps is 400 milli-amps
your device draws just 4 milli-amps normally (0.004 amps), but current peak (when the device is on max load) can go as high as 20 milli-amps (which is 0.02 amps)
your device draws just 4 milli-amps normally (0.004 amps), but current peak (when the device is on max load) can go as high as 20 milli-amps (which is 0.02 amps)
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Your device is a transducer, a transmitter or other type of control device which is controlled by an electronic controller outputting a 4 to 20 mA signal.
For instance, a transducer used with a pneumatically operated control valve, will output a 3 to 15 psig pressure to the valve's pneumatic actuator which is proportional to the 4 to 20 mA signal from the controller.This will modulate the control valve to control the flow through that valve. These devices are called analog devices.
However, the computer age is overtaking the analog system with digital signals to the transducers, The advantage being many elements of a control system can be served with one cable=pair, whereas a single cable=pair is required for each analog device.
TexMav
For instance, a transducer used with a pneumatically operated control valve, will output a 3 to 15 psig pressure to the valve's pneumatic actuator which is proportional to the 4 to 20 mA signal from the controller.This will modulate the control valve to control the flow through that valve. These devices are called analog devices.
However, the computer age is overtaking the analog system with digital signals to the transducers, The advantage being many elements of a control system can be served with one cable=pair, whereas a single cable=pair is required for each analog device.
TexMav
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'4-20 mA' means between 4mA and 20mA