The supply is 24 VDc so the output should also be 24 Vdc w.r.t Ground ?????
Can be, but must not,
the maximum load is shown in datasheet
Relay contacts 250Vac / 3A max. with resistive load.
Output can be 0...250Vac and usually used 1/2 of that with DC , ie. 0...125Vdc
Can we replace this digital temperature controller with any type of digital controller ?
New direct replacement controller must have:
-same sensor type input ( see connection 1,2,3,4)
-same output, ie floating normally open relay contact with same ratings ( see connection 8,9)
-same supply voltage ( see connection N,L1)
-look connections 5,6 , if not used, dont care
--- if used, same function must be found in replacement controller
Check parameters in old controller to find out setpoints , modes and configurations.
(datasheet pages 6...7)
Is it the thumb rule that if a temperature sensor (of any kind) is not connected with the temperature controller
OR the temperature sensor (of any kind) gone bad (open) then the output relay of the controller won't generate the output ???
Generally yes, all industrial temperature controllers should have indication and monitoring of the sensor circuit faults.
In practice, to be 100% sure of that , it is important to test this monitoring action,
after all the parameters and configurations is set for an used application .