AI845 field powered loop
What AI845 terminals should be used for the field powered loops?
there are some options like on attached.
AI845 we can use it for single/red. applications with the single/red. base plate.you can opt for the suitable one.
Since you are asking the loop powerd (Card will drive the 24V & inturn get the signal in the same 2wire)
Am attaching the manual with deffrent options for baseplate like extended or compact(when space is constraint) since u never said about which basplate(MTU) u r using, it describes how to make 2wire & non-2wire loops
Here A:Zero potential
I believe that I understood your question a little differently when you asked about using the AI845 with a "field powered" device. By "field powered" , sometimes referred to as a "4-wire device", I assume that you mean a device where the 4-20mA input is being powered by the device itself (e.g. magnetic flow meter) and not from the DCS Power Supply (e.g. DP or Temperature Transmitter) referred to as a "2-wire device".
When using the AI845 with a 4-wire field powered device, with regards to how to wire it up, particularly when it comes to the non-redundant termination base, it will depend somewhat as to which base you are using. So, the document that Hasha D. provided in the earlier response provides the examples that you need for the various option, the document that he provided clearly shows how to wire it for the 4-wire devices using the TU844/TU845.
However, because the AI845 module, just like the AI815 and AI810 modules, does not provide isolated inputs, which if you are mixing 4-wire and 2-wire inputs on the same card can lead to potential ground loop issues, we typically use loop powered signal isolators with 4-wire devices (e.g Acromag Model 651T-0600 - See the provided link for the Data Sheet). Using a loop powered signal isolator in effect makes the inputs the same as 2-wire devices from the DCS side and elimates the potential of ground loops issues. This does add cost to the "per channel price" but eliminates a lot of potential issues in the field.
Alternatively, for 4-wire devices, we also use the AI825 module, which provides 4 galvanically isolated inputs per card. The downsides here are:
- As it only offers 4 channels per card you need 2x as many AI modules
- The AI825 does not provide HART support like the AI845/AI815 module
- The AI825 does not support its use in a redundant AI module application (i.e. with TU844/TU845).
I hope that this helps/