Three-way or two-way isolation..

Hi,

During a course of my project, I have encountered a problem regarding one of my analog devices, a regulator. Oh well, its internal resistance reading should be around 250 OHMS, but upon reading, it reads to M-OHMS. Reading the manual of the regulator, it says that upon connection to a PC (programmable controller), it is recommended to seek advice from the PC maker regarding connection since its wiring is different.

The PC maker advice us to use a signal converter, converting 4-20mA to 0-10 Vdc because the 4-20mA signal of the regulator interferes with the other 4-20mA signal on the module.

I have searched for signal converter/ isolator that is commercially available & find two options: 3-way isolation converter (which isolation includes it power supply) & 2-way isolation converter (which DOES NOT include power supply isolation)

I wonder which should I use given the trouble I have written above? Can I just use 2-way isolation or the more expansive 3-way isolation? Please HELP/ ADVICE..

P.S.
There is also Passive & active converter. wheew..

You can in 99.99999% of the time use either, for single channel isolators. Either provides input to output isolation, the only difference really being that a two way isolator maintains a common between it's supply and the input (or output).

That is usually not any kind of an issue, but it can be if there is a very high common differential between the connected devices. Perhaps like one referenced to earth, and one referenced to the high side of a 600VDC buss. Another possible issue is where you don't want either input or output tied to the 'System Common' reference point.

Two way isolators can be a tiny bit noisier, but again, that's uncommon now-a-days.

rdrast said:

Two way isolators can be a tiny bit noisier, but again, that's uncommon now-a-days.

Click to expand...

What do you mean "uncommon"? No one has been using it nowadays for such troubles?

No, just that the two way isolators have one power supply (on either the input or output sides) that are directly tied to the system power. On those, noise from the overall system power supply or switchgear can show up on the analog signal.

It is uncommon today, as the actual power supplies in the isolators (and most other equipment) have become better.

I see..Understood what you mean..

Does it necessarily follow that the 3-way isolators have different supply from in to out which due to filtration reduces or eliminates noise?

theripley said:

... its internal resistance reading should be around 250 OHMS, but upon reading, it reads to M-OHMS.

Click to expand...

This thread continued?
A couple of months ago, I used one of these. When I opened the box, the unit inside was the wrong part number. I ordered a voltage type, but the one inside was current. Wonder if you got the other one. Recheck to make sure you have the correct part.
If the input resistance is not 250 Ohms, then you have a wrong part number or defective unit. Why don't you go back to the supplier and demand he sells you the correct part?

If you're stuck with it, then use a resistor. Put a 1% 500 Ohm resistor across the input. At 4-20 mA, it will give 2-10 volts.
Can you change output to 0-20 mA? That will convert to 0-10 Volts.