![]() You can also follow us on Facebook and Twitter to receive daily updates. If you liked this article, then please subscribe to our YouTube Channel for Instrumentation, PLC, and SCADA video tutorials. Watch the below video to learn the 4-20 mA basics, history, advantages, and disadvantages. catalytic gas detectors, or Infrared gas detectors using optical heating elements. The TT236 model is a space-saving 3-wire transmitter that isolates and converts a DC current or low voltage input to a proportional 4-20mA control signal. Not suitable for power hungry transmitters, e.g. Sub 4mA status signalling is limited due the reduced range of mA available between fault and a zero reading. The 2864655 from Phoenix Contact is a 2-channel, loop powered passive isolator. This configuration is not suitable for control panels that require a 0mA signal for a fault indication. Transmitter discrete fault signalling can not be set at 0mA as this configuration continues to draw some current in a fault condition.Only two cable cores are required to the transmitter.The 4-20mA signal flows through the 24V dc line and the signal line to the controller. The transmitter and control panel can use the same 24V and 0V dc supply lines. This is the most common configuration of modern 4-20mA transmitters. Current source transmitter, non isolated (3 wire) Therefore it is important to qualify whether it is the transmitter or the control system that is to be wired in a specific configuration.įor the purposes for this guidance note it is assumed that both the transmitter and the remote control panel require a 24Vdc supply. When transmitters are wired in a current source configuration it follows that the control system will be current sink, and vice versa. Check the transmitters technical manual for the available options. However some transmitters may be limited to either a sink or source configuration. Most modern transmitters can be wired in a current sink or source format, selection is often made by the use of specific terminals or the location of a link within the transmitter. The design of the associated control panel dictates which option should be used. ![]() Several transmitter wiring options exist. This supply can be derived local to the transmitter or supplied direct from the associated control panel. Transmitters typically require a 24Vdc supply. audible and visual alarms or initiate some trips or even plant shut down procedures. The control panel uses this signal and activates executive actions via relay contacts.Į.g. ![]() This signal is sent to a remotely located control panel. Gas detectors / transmitters offer 4-20mA outputs, where 4 mA equates to a zero reading and 20 mA equates a full scale reading of the calibrated range. Industrial transmitters are available for monitoring many parameters these including pressure, temperature and flow etc.
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