YSI 55 - Manual (Page 15)

11
Type 3 Errors
A. Altitude:
Operator Error: A 1000 foot error in altitude (when calibrating) is equal to an error of
approximately 3.6% at the 10 mg/L level.
Instrument Error: The maximum DO error caused by calibrating to altitude in increments
of 100 feet: ±0.18% (< 0.015 mg/L at 25°C)
B. Humidity:
Errors occur if calibration is performed at less than 100% humidity. The worst possible case
would be calibration at 0% humidity. The error varies with the calibration temperature as
follows:
Temperature Calibration Error at 0% humidity
0 o C 0.09 mg/L
10 o C 0.14 mg/L
20 o C 0.21 mg/L
30 o C 0.33 mg/L
40 o C 0.50 mg/L
Approximating The Error
It is unlikely that the actual error in any measurement will be the maximum possible error. A better
error approximation is obtained using a root mean squared (r.m.s.) calculation:
r.m.s. error = ±[1a 2 + 1b 2 + 2a 2 + 2b 2 + 3a 2 + 3b 2 ] ½ mg/L
NOTE: This sample calculation is for a near extreme set of conditions.