----- Original Message -----
From: "Rob Conway" <[EMAIL PROTECTED]>
To: [email protected]
Sent: Wednesday, November 12, 2008 3:17:04 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Owfs-developers] 4-20 ma loop
4-20mA is simply 1-5VDC if you place a 250 ohm resistor in the current loop. Use the 1wire 4 channel a/d. Please not though that the resolution of the A?D is not as specified. Its more like only 8 bit, I think the data sheet states 10 or 12 bit, somebody else posted this comment as well, didn’t believe them at the time however I now believe its true. However for your need you can get reasonable data for aqua use. I can get accuracy of
PH transmitter actual reading on the unit 6.51 1wire reading <(+/-)0.02
Conductivity actual reading 200us 1wire reading <(+/-)5
I need to sample the data a few times then average it to get a filtered reading due to the resolution and you just have to make sure your scaling is correct. i.e. ph transmitter is calibrated -4-20mA (1-5 VDC) for 5.5 – 7.5 pH thus you’ll never get the accuracy if you had calibrated it for 0-14ph = 1-5VDC it would not provide an accurate reading
Donald BTW link for temp probe http://img.photobucket.com/albums/v319/rjconway/1wire_temp-1.jpg
rob
.
-----Original Message-----
From: Donald J. Organ IV
[mailto:[EMAIL PROTECTED]
Sent: Thursday, November 13, 2008
6:51 AM
To: owfs-developers
Subject: [Owfs-developers] 4-20 ma
loop
We are looking to measure Ph and a couple of other things and have found that we will need to setup a 4-10 ma loop can someone recommend a lost cost solution to this??
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