B+K precision 5490C Series, User Manual

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5.3 Limit
The limit test allows the user to perform a Pass/Fail test. By setting the upper and lower limit values,
the results will display the amount of Low and High failures. Use the softkeys to adjust Lower and
Upper limits. Set the limits by using the cursor navigation keys and button.
5.4 dB Calculation
The dB and dB math functions apply to DC V and ACV measurements only. This function allows
measurements to be scaled relative to a reference value.
Each dB measurement is the difference between the input signal and the stored reference value (both
converted to dBm): dB = reading in dBm – reference value in dBm
The relative value must be between -200 and +200 dBm (default is 0). You can measure this value by
pressing ‘Measure Ref Value’ or input a specified value using the softkeys.
5.5 dBm Calculation
The dBm function is a logarithmic expression that compares the power delivered to the reference
resistance, relative to 1 mW:
dBm = 10 x log
10
(reading
2
/ reference resistance / 1 mW)
5.6 mX+b
The calculation of reading X on screen is performed as follows:
Y = mX + b
Where,
X is the normal display reading on the screen
m and b are the user-entered values
Y is the displayed result
5.7 Percent
If the percent calculation is selected, a reference value must be specified. The percentage calculation
is performed as follows:
Percent =
Input−Reference
Reference
× 100%

Input is the measured reading

Reference is the user-entered constant

Percent is the displayed result