I am trying to figure out what is the best practice to having multiple tag looking at the same value of a modbus address. One tag live in a folder that I use to transmit out via MQTTT and another tag live in another folder that I process for data handling. Both tags are reading the same modbus address. It is better to have one tag read the modbus address and the other tag uses a derived to look at the first tag? Or does it make no difference? Let’s say I need to to do 10,000 tags this way, does it matter? Or since this get read into the Ignition’s OPC UA engine it doesn’t matter? If both tags have difference scan rates does it make a difference in that case?
Yes. If multiple tags point at the same address in a device, and are on the same pace, they will all be satisfied together with a single request. Different pace, different request.
Phil’s correct, but it would be better if you used a reference or derived tag for the duplicate. An OPC tag, especially at the same rate, would be needless memory/CPU overhead. The only reason I can see to use an OPC tag for the duplicate is if you really don’t want the two sampled at the same rate.
Couldn’t the slower one be made to reference the faster one on its own timing ?
Thank you everyone for your input. I will use a derived/reference tag and will only use Modbus if all scan rates are the same.