YSI 85 - Manual (Page 31)

YSI, Incorporated Model 85 27
SECTION 11 DISCUSSION OF MEASUREMENT ERRORS
11.1 DISSOLVED OXYGEN MEASUREMENT ERRORS
There are three basic types of error. Type 1 errors are related to limitations of instrument design and
tolerances of instrument components. These are chiefly the meter linearity and the resistor
tolerances. Type 2 errors are due to basic probe accuracy tolerances, chiefly background signal,
probe linearity, and variations in membrane temperature coefficient. Type 3 errors are related to the
operator's ability to determine the conditions at the time of calibration. If calibration is performed
against more accurately known conditions, type 3 errors are appropriately reduced.
The sample calculations that follow are for a near extreme set of conditions.
TYPE 1 ERRORS
A. Meter linearity error: ±1% of full scale reading, or ±0.15 mg/l
B. Component and circuitry error: ±0.05 mg/l
TYPE 2 ERRORS
A. Temperature compensation for membrane temperature coefficient: ±0.03 mg/l
B. Temperature measurement errors: A maximum ±0.2
o
C probe error is equal to ±0.14 mg/l