Yokogawa Button Operated DX2000 - Manual (Page 12)

11
Computing example of the display value accuracy
¾ Integration time 50 Hz
¾ 2 V range Voltage span 0.0000 to 1.0000 V
¾ LOG span -2 to 3
1) Determine the converting equation for the setting.
• Y = 10 (SU-SL)*(X-VL)/(VU-VL)+SL
= 10 (3-(-2))*(X-0)/(1-0)+(-2)
= 10 (5X-2)
2) Determine the measurement error with respect to the input voltage.
• Measurement accuracy of the 2 V range = ±(0.05% of rdg + 12 digits)
= ±(0.0005*10000+12)
= ±17 digits
• Therefore, for an input voltage of 1 V, the value will fall within the range
between 0.9983 V and 1.0017 V.
• Since the computation is performed on the negative side with large error in
the LOG characteristics, we obtain X
err
= 0.9983 V.
3) Determine the hardware error of the display value.
• Substitute X
err
, the value determined in 2), into the equation of 1).
Y
err
= 10 (5*0.9983-2)
= 9.8 * 10 2 (truncate values below the one-hundredths place)
• Since the true value is Y = 1.0 * 10 3 , the error is 2 digits.
• Therefore, the hardware error of the display value is given by Y’ = ±2 digits.
4) Display value accuracy of the mantissa
• As a final error, we add the software error to the hardware error.
• Software error = Hardware error * 1.1 + 1 digit
• Display value accuracy = ±(2 digits * 1.1 + 1 digit)
= ±(3.2 digits)
• The fraction is rounded up. When the mantissa is 2 digits, the display
accuracy is ±4 digits.