analog I/O device connection to PC - question - Page 1
Forum section: electronics / projects

author: morty3
author_rank: Newbie
timestamp: July 15, 2015, 02:39:08 pm
content: Purchased an older model gas calibration device (still brand new in box after 15 years) and wanted to link to PC so I can log and chart the concentration levels.Searched around a bit and found a few different freeware logging software choices, and decided on C-LOGGER by Contec since there seem to be a variety of USB and PCI supported devices, and seems to fit and is professional looking, etc..Anyways, will attach pic what the old school terminals looks like from the back.Wanted to double check with someone who understands electronics better than I do to see if the device I picked out will work?The manual (from calibration device) states the following specs:Output and Control TerminalsAnalog Outputs:The output signals are updated about 14 times per second.The voltage output is an isolated voltage signal 0 to 10 V, proportional to the concentration (actuallythis signal swings down to about -0.25 V below zero).Input resistance of the load should be higherthan 1 kW.The current output is an isolated current signal 4 to 20 mA, proportional to concentration.Inputresistance of the load should be less than 650 W(optional 1350 W). The current output provides theenergy for the current loop. Attention: The current output must not be connected to an external power supply !This is the device by Contec I was planning on using:http://www.contec.com/product.php?id=355And here is the data sheet for that:http://www2.contec.co.jp/prod_data/adi128usbgy/adi128usbgy_e.pdfHere's my question: Will this device work for my needs? I am confused by the input resistance numbers"Input resistance of the load should be less than 650 W" and "Input resistance of the load should be higherthan 1 kW" I checked with the manufacturer who is still in business but because I asked too many questionsabout the device (they wanted to sell me a new one @ $5000) and they stopped answering. : )The spec sheet for the Contec USB device states input impedance of put impedance of 1M OHM (Min.)Maybe I should just try it and see but don't want to potentially damage the unit.Voltage seems to match (plus or minus 10 volts) and looks like it can handle the current.Thanks for anyone's input, greatly appreciated.Cheers, Morty

author: amyk
author_rank: Super Contributor
timestamp: July 15, 2015, 03:32:49 pm
content: I've never seen resistance measured in watts... lol watt?If they really mean ohms then 1M > 1k so you should be ok.

author: bktemp
author_rank: Super Contributor
timestamp: July 15, 2015, 03:40:32 pm
content: Quote from: amyk on July 15, 2015, 03:32:49 pmI have seen this several times. This is a common problem with different character sets. If the charset is not displayed correctly the Omega character will be displayed as W.If you see a resistance specification with W at the end, you can be sure it was Ohm originally.

author: morty3
author_rank: Newbie
timestamp: July 15, 2015, 03:46:40 pm
content: Thanks amyk and bktemp!Yes then that makes sense! Mystery solved! Yay!Ok, one more quick question:Would 12 bit be plenty for this purpose then? There is also a 16 bit unit but the 12bit one I found seems to be in better shape.In other words, would there be any noticeable difference given the signal is only updated 14 times a second?If so then perhaps better to get the 16 bit unit?Thanks! Morty

author: morty3
author_rank: Newbie
timestamp: July 15, 2015, 04:32:59 pm
content: OK, I found this which seems to be relevant. Since my total range is 20MA total perhaps better to choose 16 bit unit forpotentially greater resolution.http://labjack.com/support/faq/what-does-12-or-16-bit-resolution-meanDoes that make sense?Thanks very much.. Morty