I have a set of digital and analog I/O coming from a source that has it's own power source and enclosure that the PLC (honeywell HC900) is not a part of. (microwave system powersupply/controller cabinet that the honeywell will be interfacing via DI/DO and some 0-10V analog signals (in and out). What would be a good way to make sure the PLC reads these at all times without any issues.

My idea at the moment is, that since my electrical enclosure will be powering (480VAC) and will be grounding the microwave systems, that I bond the 0V of both the PLC's and microwaves 24VDC supply as well to the same ground. Though, I feel iffy about the 10VDC analog I/O still. I am used-to 4-20mA signals only.

Does this seem bullet proof?

 

Analog Inputs
Honeywell offers 2 choices for analog input modules (universal (mA. V, RTD, T/C) and hi-level (mA or V).

I've found Honeywell AI modules have great isolation. Galvanic isolation spec for both AI cards is 400 VDC point to point; 1K VDC input to logic (back plane).

Both use a 15 bit A/D. One major difference is the universal input updates at only 500mS max, compared to 100mS update rate for the 16 point hi-level card (when used with an 'S' (SIL2) version CPU rated for 10Hz update).

The hi-level card also has 0.1% FS reference accuracy vs the 0.2% FS accuracy for the universal card.

Analog Outputs
There's 3 choices for analog outputs. 4 point, 8 point, 16 point.

They're primarily used for current outputs and do not source voltage directly, you'll have to use external, precision 500 ohm dropping resistors on one end or the other with a 0-20mA configured output to get the 0-10Vdc. If it were me, I'd put the resistor on the AI end and drive current through the loop for best performance, rather than generating the voltage at the AO and picking up noise over the run to the AI.

Two of the three (8pt and 16pt offer the option to power the module from an external DC power supply. The 4 point module uses only the rack's internal power supply (5V and 24V sources).

4 point card has 500Vdc isolation channel to channel and 600Vdc input to backplane logic isolation.
8 point and 16 point cards have channel to backplane 500Vdc isolation, but use 4 point/channel groups, with no isolation between channels in a group. Group-to-group isolation is 500Vdc.

AO cards generate heat and the number of cards per rack limits are 10 per rack for the 4 channel cards, 4 per rack for the 8 channel cards and 2 per rack for the 16 channel cards.

If your analogs on the other end are anywhere near ground, the Honeywell cards will work OK. But you can't float one end to 480Vac above ground because that'll fry anyone's analog on the other end.