More -- oozing on the muggy shore of the gulf coast [email protected]
--- Begin Message ---Douglas McMurtrie wrote: > > Tai-Pan wrote: > > > > For those who weren`t around back when we all started using TDS-1 > > testers. :-) > > Tai-Pan wrote: > > > > > > Greetings all you CS makers and users. > > > Was reading the postings of Ringdance on Wed 1 Apr, and Fred on 2 Apr > > > about their TDS-1 testers. Douglas wrote: > Question regarding the TDS-1. I've just placed an order for the Hanna > DIST-1 which is a bit more expensive than the TDS-1. The reason that I > did so was because the specs on the TDS-1 claimed a margin of error of + > - 10 ppm. Not good if we're trying to measure in the 1 - 50 ppm range. > Big diff between 5 ppm and 15 ppm. The DIST-1, however, has a margin of > error of 2% flat across the scale. That means that at the top end of > 2000 ppm it will be + - 40 ppm and down in our range of interest it will > have a margin of error of + - 1 ppm at a 50 ppm concentration. I > confirmed all this with the tech specialist at Hanna. Did I miss > something here? I don't see how one could have confidence in the TDS-1 > readings at very low ppm concentrations. Hi Douglas and list, Lets look at some numbers here. TDS-1 , Max range 999ppm , Accuracy + - 10ppm, Resolution 1ppm DIST-1 , Max range 2000ppm , Accuracy + - 40ppm, Resolution 4ppm Now for the TDS-1 we have 10/1000(999)= 1% of full scale accuracy. For the DIST-1 we have 40/2000 = 2% of full scale accuracy. We see that both instruments have the accuracy as stated in their spec sheets. The TDS-1 is twice as accurate as the DIST-1. Its resolution is four times better. ADJUSTMENT: If you wish to read at the low end, you calibrate it at the low end. If you wish to read at the high end, you calibrate at the high end. For the TDS-1 this means that at 1% of full scale if you cal it at 1ppm it will be within 1% at the high end or + - 10ppm of 999ppm. Or it means that if you cal it at the high end (say 999) it will be within 1% at the low end or + - 10ppm of the low reading . That is why it has a cal adjustment. Mine is calibrated for the low end since most of my reading are there. Accuracy is misunderstood by many people. A gun is accurate if it puts the bullet in the same place all the time, not in the bulls eye. If it shoots a good group its accurate. Now you can adjust your gun to put the group where you want it(in the bulls eye), that doen`t change its accuracy. Thats what calibration does(moving the group). If we calibrate at 001ppm and the resolution is 1ppm thats really on the money. As we read further up the scale the ppm will slowly get more and more off until we get all the way to the top(high end) where it could be as much as + -10ppm off (but still within 1% of full scale). Hope this helps a bit. Bless you Bob Lee -- oozing on the muggy shore of the gulf coast [email protected] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the subject: line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
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