Specifications

This document lists specifications for
the Agilent Technologies 34970A Data
Acquisition/Switch Unit and its mod-
ules. 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 actu-
al measured value and range is the
name of the scale (1V, 10V, etc)—not
the full scale value (1.2V, 12V, etc.).
• DMM measurement accuracies
include all switching errors.
Switching errors are also listed sep-
arately in the module specifications
section. Temperature measurement
accuracies include ITS-90 conver-
sion errors. The thermocouple accu-
racies include the reference junc-
tion error as well.
• Accuracies are listed as either
24-hour, 90-day, or 1-year specifica-
tions. This refers to the length of
time since the instrument’s last cal-
ibration. 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°C - 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) = 365µV,
for a total accuracy of
365 µV / 9 V = 0.0041%.
EXAMPLE 2: Extreme operating
temperature
When the 34970A is used outside
of its 18ºC-28ºC 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 oper-
ating range for additional error:
(0.0005% reading + 0.0001%
range)/°C x (35°C - 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—
just add the listed measurement accu-
racy 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
1.0°C + 1.1°C = 2.1°C 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%.
Agilent 34970A
Data Sheet