how many HMI can be connected to ML1100 at once on Ethernet.?

Thanks Andrew

That answer is quite subjective Andrew. The ML 1100 Specifications are going to tell you that the the 1100 supports a fixed number of ethernet connections. I don't have the spec handy but I think it is either 32, 48, 64 or 100. This represents the number of connections not the the number of HMI's.

If we choose a number of connections as out specification say 100 for the sake of discusson. Then each HMI will consume a minimum number of connections depending on brand and its design. Not having that spec lets say each HMI consumes 4 conenctions with is quite common for the average HMI running an average program. This would appear to give you 25 connectable HMI. But then there is a caveat that at higher load levels performance my degrade. In other words, you canconnect 25 HMI's in our example if you are willing to wait 30 seconds for a button press to turn on a light. So factoring in a performance quotient of 60% and this is quite average from my experience we actually can connect only 13 HMI's and get acceptable performance even though the nubers and specs say 100 connections and 25 HMI.

hope this helps once you start looking at actual specs.

Bob provided a good answer for concurrent connections to the PLC. You can get around this by using an HMI package that uses a number of PLC connections that itsn't based on HMI runtime clients (distributed or web based). Granted these software packages may be a bit heavy hitting for a Micro, but it's good info that's applicable for any PLC series.

Adding concurrent HMI clients will not add connections to the ML in a well designed distributed HMI. It won't add read traffic if it's reading the same values that the other clients are. Obviously if a client is reading a new tag range, that will cause a PLC read. Writes should occur as if they were coming from any HMI node.

This is how FactoryPMI with SQLTags works. RSView SE should work that way as should the heavy hitter "distributed" version of Intouch.