ML1400 vs Compactlogix L23E

[Ken Moore 23]

Have a small application in the works, ethernet is a must for historian connectivity. 12DI, 14DO., and 4 AI (4-20mA). HMI will be a G310C. The ML1400 would be cheaper, but I was going to buy a1762-IF4 for the analog inputs, since the ML1400 is setup for voltage only. Since this is a new app. I thought the L23E might be better, latest and greatest etc..... However when reading the specs. I noticed that the analog inputs on the L23 are only 8-bit. Am I reading this correctly?

[mercedes98 0]

I'm not sure which processor you will use but I think it is this one: 1769-L23E-QBFC1B I hope this link down here will give you more information on this processor. http://literature.rockwellautomation.com/i...qr011_-en-e.pdf

[TimWilborne 108]

That's what page 49 tells me although I haven't used on yet http://literature.rockwellautomation.com/i...in082_-en-p.pdf As much as I would love to talk you into getting this controller so I could get your opinion on it, it seems the criteria you have laid out is right in line with the Micrologix 1400. Really, if you aren't going to do I/O messaging and your plant isn't requiring use of the Controllogix/Compactlogix platform, what would be it's advantage in your application besides the "want" factor?

[Ken Moore 23]

You guessed correctly, the want factor is high, plus I think the programming would be slightly easier with the L23. The application is a self cleaning filter, it has a scraper that moves up and down (pneumatic cylinder with limit switches) on a timed basis until the DP (differential pressure across the filter) reaches setpoint one, then the scraper is sped up a tad, if the DP reaches setpoint two, a flush valve is cycled and the scraper goes a littler faster, if the DP is still high after the flush and a time delay, a visual alarm is activated, if the DP reaches setpoint three, the supply pump is stopped and an additional visual/audible alarm is activated. There are 4 such systems, with one common controller. The G3 will allow the operator to pick a product from and menu, and the timer values will be loaded for that product, along with the three setpoints. Different products have different setpoints because of rate and viscosity. I've already decided to go with the ML1400, I just need to add the AI module and a OX6I for the pump starters. The cost will be about half what a L23 would run me. BTW, when I called the local rep. about the G3, I got a very good response. I harped on the lack of support once before, but now things are much better.

[TimWilborne 108]

At the same time, your situation is a little bit unique in that most all your applications are critical. If this application would be the only one that would allow you to evaluate the L23 in a non-critical application, the opportunity cost could be high enough to justify it for future critical applications Glad to hear you got better support from your G3 distributor. Let me know if I can help you out

[finfin 0]

as far as the "voltage only" inputs: we commonly use these with a 499ohn precision resistor across the inputs. This causes the current transmitter to develop the proper voltage for a voltage input. 20 ma across 500ohms is 10 volts. 4 ma is 2 volts.

[JesperMP 2]

Be sure to check the max resistive load on the output from the sensors you intend to use. For 2-wire 4-20mA sensors, at 24V it is quite common with a max around 500-600 ohm. At lower voltages the limit for output load is correspondingly lower. So 500 ohm may be a bit close to the limit, depending on the sensors used. When I have done something similar, I have used a 250 ohm resistor.

[Ken Moore 23]

Yes we have used the 250ohm "trick" in the past to get 1-5 volts from a 4-20mA device. However, that was in the "good old days", when we did not have a choice. In today's world, I/we always try to get I/O modules that do not require any tricks. A few hundred dollars for a true current card, is well worth it, this way I do not have to worry about a late night maint. swapping out a transmitter, and using the wrong resistor, or none at all.