This allows a greater flexibility and more possibilities for your wiring.
Limit of the relay contact output: While it will work great in numerous process, you have to bear in mind that a relay contact output is mechanical and quite slow: this is partly due to a setting which limit the switching over a given period of time (time constant) in order to enhance the life time of the relay (the number of operation of each mechanical relay is limited: our relay output are certified for over 10 million operations for example). This is usually fine for temperature because of the temperature lag. However if you require a fast operation on the output you should consider a 4-20mA or a SSR drive output.
Voltage or current signal
A voltage output will typically deliver a 1-5V signal and a current output will typically provide a 4-20mA signal.
Other possible signals can be 0-5V, 0-10V, 2-10V (Voltage), 0-20mA (current).
Please note: On our Fuji PXR temperature controller, only 4-20mA output is available. For voltage output signal (such as 1-5V or 2-10V) please see our process controllers PXG
Voltage and current output are used to drive a variety of devices in a very accurate way. 4-20mA is an industry standard and lot of devices will accept that as an input (see our Watson Smith I/P converters for example). The signal can vary from 4mA and 20mA and therefore it allows an analogue control much more accurate than that of a simple on/off control you would get with a mechanical relay contact output.
Solid State Relay (SSR) drive output
For an accurate control, SSR control (solid state relay) are preferred over standard relays.
The SSR drive output of the controller will provide a fast Voltage signal. For an "off" signal, the voltage will be closed to 0Vdc. "On" will provide a signal around 24Vdc, depending on the controller. As an example, Fuji Controllers provide 17 to 24Vdc for "on" and 0.5V or less for "off".
This will be the signal for an external Solid State Relay (sold separately in most cases). This SSR will have no moving parts, allowing it to switch on/off extremely quickly and thus following the Voltage signal from the controller. It also results of a greater lifespan.
There are lots of Solid State Relays available with different specifications - the most basic one being the rating (see "current rating" on the "Relay contact output" paragraph). If you want to discuss your application please do not hesitate to contact us.