scadametrics

Ken, I have an example that demonstrates the CPW command on a ML-1400. The example is basically doing what I believe you are trying to do... combining two adjacent N-registers into a (long) L-register. See page 3 on this document: http://scadametrics.com/PDF/App_Note_002.pdf Hope this helps! -Jim.

Steve, If you are using a water meter that is compatible with my company's 'EtherMeter' water meter interface (eg Sensus, Neptune, Badger, etc...), then it's possible that you could use our device to read the total gallons directly from the meter register. Our device can communicate total & flow from most AWWA-type water meters to your L32E via EtherNet/IP or DF1. It also translates into Modbus, but in your Allen Bradley situation, EtherNet/IP or DF1 would be most convenient. Also, we have a nice application note for using the EtherMeter with the L32E.

Red, Rather than a PID loop for feedback temperature control, you may be able to achieve success with more of an open loop control approach. If you probe for the temperature of both water sources, then you should be able to calculate the desired ratio of city water flow to chilled water flow. But you will need to know the instantaneous flow rate of both city water and chilled water, so you will need to add a flow meter to each source, because you will have to adjust the two valves to achieve the desired mixing ratio. Now for the valve adjustments, you will probably have to do PID control of each valve to achieve target flow rates. By open-loop for temperature control, I mean that the measured temperature of the mixed water will not be part of the control calculation in this case. But of course the measured temp would be available to verify the success. Just another approach to consider. Hope this helps!

If you want to build DLxx cables very inexpensively (~$8)... Buy one of these RJ12 cables: http://www.l-com.com/search.aspx?q='td...9;&join=All eg TDC027-2 And buy this: http://www.l-com.com/item.aspx?id=2447 (db9-female) or http://www.l-com.com/item.aspx?id=2449 (db9-male) Then configure the plug-in pins, and you're set. That's how we make our DLxx cables at my company. Hope this helps!

Since you've already gone to the trouble of generating a table of flow versus pressure, you could also create your own formula by creating a curve-fit function.

I had the same thought as pfort... I'd look for a DC drive. It should do what you are looking for.

Jhughes, There are other laboratories besides UL that work from the same UL standards (in this case, UL508A). NRTL is the proper term that describes all of them (Nationally Recognized Testing Laboratory), and each NRTL receives their credentials from OSHA. I personally use MET Labs (Baltimore, MD), and I recommend them without reservation. Also, if you plan to build your own panels, I don't see how you can avoid buying the standards documents. You'll definitely need them. But I'd shop around... There are many places that sell the same standards documents online but I've seen widely varying prices.

I don't know if this information applies to this particular PLC question, but I've found (the hard way) that some USB-Serial converters don't support anything except 8 data bits, 1 stop bit, and no parity. The one I was trying to use in a control application allowed me to specify even or odd parity (without complaining), but it just didn't implement it.

Pulsar, I'm not an expert, so I hope someone else will weigh in on this, too... But with a NET-ENI, you can still have a large number of PLC's together on the same network. But I believe the 4 device limit refers to the number of active TCP/IP sockets that the unit supports. I think this means that a single NET-ENI will allow the SLC5/04+NET-ENI to have a maximum of 2 peer-to-peer connections with other PLC's on the network. You could increase this by going with a different type of gateway device instead of the NET-ENI, such as the Digi One IAP, which allows up to 64 peer-to-peer connections, which is another option. Will each PLC be talking via message instruction to every other PLC on the network? If so, then yes -- you will need more than the 2 connections. If not, then you may be OK. Hope this helps! (Edit: After switching to linear view, I just saw Bob's response that explained it better than I could.)