Conductivity Meter Specification - What Is Accuracy +/- 1% Full Scale + 1 digit

Dongzkie

Involved In Discussions
#1
I have read the specification of a conductivity meter.
Accuracy +/- 1% Full Scale + 1 digit , what does this means? please if anyone can give a brief explanation.
 
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Jerry Eldred

Forum Moderator
Super Moderator
#2
This means +/- 1% of the full scale value, regardless of what point in scale a measurement is made. For example, on a meter with a 0 - 100 scale Volts DC, +/-1% of full scale is +/-1Volt DC. Then, even if you are making a mesaurement at 10, 25, 50, 75 or 100 Volts DC, the tolerance in that example would be +/-1 Volts DC.

When you add +/-1 least significant digit to the specification, this is added to the above tolerance. So in my second example, lets use the same meter as above (0-100 Volts DC), and we will say the least significant digit in the display is 1 Volt DC. When you add the +/-1 from the first example to +/-1 digit, the total tolerance is now +/-2 Volts DC. so regardless of what reading is involved, the total tolerance using +/-1%FS +/-1 LSD, is +/-2 Volts DC.

Tolerances for the above readings would be 10 +/-2VDC (8 - 12 VDC); 25 +/-2VDC (23 - 27 VDC); 50 +/-2VDC (48 - 52 VDC); 75 +/-2VDC(73 - 77 VDC); 100 +/-2VDC (98 - 102 VDC).

If the resolution on the meter had been 0.1 VDC, the total tolerance would have been +/-1.1 VDC.
 

BradM

Staff member
Admin
#3
Wow! Great answer as usual, Jerry. :applause:

Dongzkie, if you are wanting to calculate total error, don't forget about the error with the sensor and such. :agree1:
 

Dongzkie

Involved In Discussions
#5
Thank you sir :tg:
But i have two more questions, what is conductivity range and the resolution mean, see below.

 
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Jerry Eldred

Forum Moderator
Super Moderator
#6
This would be calculated essentially the same way as I explained above for including resolution. Instead of +/-1 least significant digit being added, +/-0.05% of the full scale amount would be added. In your posted specification table, for example, one of the included ranges is 199.9 mS/cm. Using that range, 0.05% of full scale = 0.05% X 199.9 = 0.09995; which in this case would be rounded to 0.1 (due to the resolution of the meter).

You should add all of the cumulative tolerances together before rounding though. Also, don't forget that when determining total tolerance for a given measurement value, add all of them together.
 

Dongzkie

Involved In Discussions
#7
@jerry
sir thank you very much for the explanation.
I have a standard solution which is 1411+/+4µS/cm, in this case I have to choose in the conductivity range of 200 to 1999µS/cm?
Thanks
 
N

NTAinc

#8
@jerry
sir thank you very much for the explanation.
I have a standard solution which is 1411+/+4µS/cm, in this case I have to choose in the conductivity range of 200 to 1999µS/cm?
Thanks
According to your spec sheet, the meter can auto-range, or select the range needed automatically. But for the solution you listed, the meter would be in that range (200 to 1999 us/cm). The accuracy of the meter in said range would be 1999 * 0.01 = 19.99 plus 1 (1999 * 0.0005 = 0.9995) or when all rounded, +/-21 us/cm. I am guessing that the solution you gave is being used to calibrate the meter (since one of the automatic calibration points is 1413 us/cm) and not the other way around (the meter is far more inaccurate than the solution). I would conclude that that would be acceptable since you have a TUR of about 4:1 (there may be a small, additional uncertainty component for the fact that the nominal value of the solution is not exactly the same as the meter's spec). Hope this is was helpful.
Tessa
 
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