MicroLogix 1400 Input Question

[mhowasso 5]

Hi All, Im using a MicroLogix 1400 with a 1762-IQ8 Input Module. I think the module input is good for 8ms. I want to connect a OMEGA FTB4705 Flow Meter that has an sinking ouput pulse of 550 pulses per gallon. The flow rate is about 10 gallons per minute. How can I calculate the flow rate pulse frequency to determine IF this module is fast enough to work. Im sure it is simple, but Im dont know. Thanks, Edited 26 Jan 2013 by mhowasso

[b_carlton 61]

10 gallons/minute * 550 pulses/gallon = 5500 pulses / minute 5500 pulses/minute / 60 seconds/minute = 91.666 pulses/second Inverting gives 0.0109 sec/pulse or about 11 milliseco0nds. If one pulse (ON plus OFF time) is 11 milliseconds then the ON or OFF time is about 5.5 milliseconds. You probably aren't going to make it. Your program scan time also would have to be less that either the ON or OFF times. I think you'll need a high speed counter.

[machspd 0]

550*10gal.=5500 pulses per 10 gallon.. 5500/60 seconds= 91.7 pulses per minute. 60sec./.8ms=75 scans per minute. If you can change the millisecond time on the ml1400 to .6 seconds this would give you 100 scans per minute thus freq. pulse should be set at 92%.. I think... not sure you can take the scan time down on a ML1400.. Can someone verify? my math was never very good.. Hope this helps.

[mhowasso 5]

Thanks to you both for the help. It looks like I might be asking too much for this module. I would like to use the HSC on the base of the 1400 but I believe it will only except sourcing signals and not sinking. Is there a device that you would recommend that would convert the sinking to sourcing or is there another option you could recommend..?? Thanks

[Mickey 71]

See picture from manual. And link to convert if you want. http://uk.rs-online....ioning/5329980/ Edited 26 Jan 2013 by Mickey

[mhowasso 5]

Hi Mickey, You know at first I thought the same thing too, then I tried to verify this with AB Tech Support chat room and the guy told me no, that was only on 1200 and 1500, he even sent me a tech note. So thats what led me to the IQ8 module. I tried what you said and YES it does work..!! Now I should have the ability to use the HSC feature on the base of the 1400. Thats why I hate bothering you all with what may seem trivial matters, but sometimes this is where I get the best answers. Thanks Again PS. It also seems the terms Sinking and Sourcing vary from vendor to vendor of devices..!!! Edited 27 Jan 2013 by mhowasso

[Mickey 71]

It's a very confusing subject. See link below. http://www.patchn.com/index.php?option=com_content&view=article&id=57:npn-pnp-devices-and-connections&catid=20:plc&Itemid=118