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21
)
ln(
b
a
b
a
ab
N
N
q
kT
V
V
V
Where K=1.38
×
10
-23
J/K is Boltzmann's constant. T is the temperature in
°
Kelvin;q is the elementary charge of 1.60
×
10
-19
Coulomb. It's found that from the formula, the contact potential depends on the nature of the metal and the temperature of
the contact surface.
If two dissimilar metals contact, the electromotive force at the contact point will plus a slowly changing millivolt level.
This kind of noise is sensitive to temperature. This noise is typically at very low frequency because the temperature of the
detector and experiment generally changes slowly. This effect is large on the scale of many detector outputs and can be a
problem for low frequency measurements, especially in the mHz range.
Solutions to minimize thermocouple effects:
1) Hold the temperature of the detector or experiment constant.
2) Use a compensation junction.
1.12
Aux In/Out
There are four 16-bit high-precision AUX-ADC input channels in SE2031. The input voltage ranges from - 10 V to + 10
V and the minimum resolution is 0.3 mV. The sampling rate was 108 KSPS. This 4 ADC channels can clamp the input
signal and amplify the internal differential signal. The input impendence is 1 M
Ω
. At the same time, they can pick up
signals to measure slow analog signal or DC signals (the signals come from temperature sensor and pressure sensor). This
is useful to proportional operation and transfer the data to the computer.
Because of the internal special structure of the 4 AUX-ADC channels, the measurement result is about 2.048V when the
input is floating.
There are also four 16-bit high-precision AUX-ADC output channels in OE2031. The output voltage ranges from - 10 V
to + 10 V and the minimum resolution is 0.3 mV, Data refresh rate is 96ksps.
The AUX IN and AUX OUT ports use standard BNC connect on the rear panel. The number display setting for AUX
ADC/DAC can be made in the [display] / [AUX OUTPUT] submenu.
1.13
Sweep Frequency and Amplitude of Signal Generator
The SE2031 adds some new functions, such as frequency and amplitude scanning. Signal generator can scan on the output
amplitude and frequency. Uses can scan on the frequency they interested in and analyze the characteristics of the signal
better. The output of amplitude scanning is sine and this will increase the scope of application.
The basic way of frequency and amplitude scanning is setting the value of the start and end point, and increasing the value
by step and then the scan is over. See more details in the sections related to frequency and amplitude scanning.
