Help with a SNAP-AOV-25 module

I am using the SNAP-AOV-25 to give a 0 - 5 VDC output to a thyristor for a heater control.
I have used a SNAP-AOV-5 previously to do this job but the current project needed to use only 1 rack because of space limitations.
The SNAP-AOV-5 is working fine with no problems at all, however the SNAP-AOV-25 is not working as I expected.
The 5 VDC supply to the AOV-25 is the same configuration as the AOV-5, in other words it is looped through the +ve terminal on the module (terminal 2) and out (terminal 3) to the thyristor and back to the -ve 5 VDC.
I would expect the AOV-25 to be able to adjust the voltage between 0 and 5 VDC as this is what is set up in the software via the ranges. Unfortunately there seems to be no control at all from the card
(0 - 5 VDC is equal to 0 - 100% output).
Testing the output of the card gives me 5 VDC continually and it gives that voltage on all of the terminals on the module.
Why is the 5 VDC output from the card not regulated in any way (0 - 100% output) and why does each terminal give 5 VDC.
Any help would be greatly appreciated.
Kindest regards

These modules are powered from the rack. Why do you have a power supply connected to them?

As @philip said, these cards are powered from the rack, no external supply needed.
Here is how to hook them up;

Thanks for your replies.
Yes I get that now, i think the PDF instructions could be a little clearer.

Just as a note, the basic standard for analog voltage outputs used to be self powered.
Therefore this is why you only see field instruments with analog volt out are self powered and are also 3 or 4 wire. In fact, unless a voltage output device has a V+ terminal on it, or some other power source (like the rack in the case of modules) it’s probably not voltage out.