Datasheet

Page 15
Find us at www.keysight.com
Spec interpretation guide
The following pages list the technical specifications for the
Keysight 34970A/34972A Data Acquisition/Switch Unit and its
modules. The explanations and examples below are helpful in
understanding how to interpret these specifications:
– Measurement accuracy is specified as percent of reading plus
percent of range, where reading is the actual measured value
and range is the name of the scale (1 V, 10 V, etc.)—not the
full scale value (1.2 V, 12 V, etc.).
– DMM measurement accuracies include all switching errors.
Switching errors are also listed separately in the module
specifications section. Temperature measurement accuracies
include ITS-90 conversion errors. The thermocouple
accuracies include the reference junction error as well.
– Accuracies are listed as either 24-hour, 90-day, or 1-year
specifications. This refers to the length of time since the
instrument’s last calibration. Use the specification that
matches your calibration cycle. The 24-hour specifications
are useful for determining short-term relative performance.
Example 1: Basic dcV accuracy
Calculate the accuracy of the following measurement:
9 V dc input
10 V dc range
1-year accuracy specifications
Normal operating temperature (18 - 28°C)
From the following page, the 1-year accuracy is:
0.0035% of reading + 0.0005% of range
Which translates into:
(0.0035/100 x 9 V)+ (0.0005/100 x 10 V) = 365 µV
For a total accuracy of:
365 µV/9 V = 0.0041%
Example 2: Extreme operating temperature
When the 34970A/34972A is used outside of its 18 - 28°C
temperature range, there are additional temperature drift errors
to consider. Assume the same conditions in Example 1, but at a
35°C operating temperature.
The basic accuracy is again:
0.0035% of reading + 0.0005% of range = 365 µV.
Now, multiply the 10 V temperature coefficient from the following
page by the number of degrees outside of operating range for
additional error:
(0.0005% reading + 0.0001% range)
/°C x (35 - 28°C) =
(0.0005% reading + 0.0001% range)
/°C x 7°C =
0.0035% reading + 0.0007% range = 385 µV
Total error is then:
365 µV + 385 µV = 750 µV or 0.008%
Example 3: Thermocouple measurement accuracy
Calculating the total thermocouple reading error is easy with the
34970A/34972A—just add the listed measurement accuracy to the
accuracy of your transducer. Switching, conversion, and reference
junction errors are already included in the measurement specification.
For this example, assume a J-type thermocouple input reading 150°C.
From the following page, total error is:
Thermocouple probe accuracy + 1.0°C
The probe vendor specifies accuracy of 1.1°C
or 0.4%, whichever is greater.
Total error is then:
1.0ºC + 1.1ºC = 2.1ºC total, or 1.4%
Example 4: acV accuracy
The acV function measures the true RMS value of the input
waveform, regardless of waveshape. Listed accuracies assume a
sinewave input. To adjust accuracies for non-sinusoids, use the
listed crest factor adder.
For this example, assume a ± 1 V square wave input with
50% duty cycle and a 1 kHz frequency.
Accuracy for 1 V, 1 kHz sinusoid is:
0.06% reading + 0.04% range
A 50% duty cycle squarewave has a crest factor of
Peak value / RMS value = 1 V / 1 V = 1
From crest factor table, add:
0.05% of reading
The total accuracy is:
0.11% of reading + 0.04% of range = 1.5 mV or 0.15%