4.7. Preconditions for correct connection and correct
settings of the input of the ADC E-502.
Simplified examples of connection of the ADC input are given in section
, however,
!
... if you do not take into account the electrical properties of the signal sources, wires (cables)
when using E-502 ADC connections, use the default E-502 program settings, then, most
likely, you will get a bad result. Why? What do you need to consider? – If you answer below
these questions, links to the Internet resources of the site
4.7.1. The physical causes of possible problems
Physical cause #1. The wide
bandwidth of ADC transmission in E-502 (about 10 MHz)
can
be not only a big advantage of ADC E-502 (in the ability of the ADC to qualitatively digitize high-
speed dynamic processes), but it can be a big problem if:
•
the signal source has an unlimitedly wide frequency band (much wider than the width
of the frequencies of the useful signal)
•
unscreened connection is applied (or the signal source itself has a significant area of
the unscreened surface), in a situation where electromagnetic fields in the frequency
band up to 10 MHz are always present in the real situation, and also in the situation of
the user's failure to apply a differential connection (and adjustment to the differential
mode), and therefore use the valuable property of a differential input – effectively
suppressing common-mode interference.
Physical cause #2.
The high frequency of the 2 MHz channel switch (when tuned to multi-
channel mode) with E-502 default settings may not only be a big advantage of the ADC E-502 (in the
high-speed ADC input interrogation), but it can also be a problem because of the measuring circuit ,
it takes a short signal setting time (less than 500 ns after the switch's own charge is injected into the
measurement circuit). This cause is fundamental for all ADC with input commutator, manifested as
a switching disturbance.
4.7.2. Conditions for correct E-502 connection and settings.
1.
If you need to use no more than 16 ADC channels, always select the differential
connection mode and E-502 settings.
2.
With a differential connection, the X and Y circuits of each channel always lead in pairs
(twisted pair, shielded pair).
3.
E-502 signal circuit should be shielded. On the screen connection, see
4.
For differential connection, when using a pair cable, to maximize the common-mode
rejection of the E-502, the output impedances on the side of the remote source along the
X and Y circuits must be balanced (connection example - p.
5.
The AGND E-502 circuit should be connected to the common wire circuit of the signal
source (if there are several signal sources – to the common junction point of the signal
source common wires).
6.
If you need to configure the E-502 for multichannel operation, you first need to optimize
the signal-to-noise ratio of the ADC in a single-channel operation mode with a
maximum data rate of 2 MHz, in which in the signal spectrum you will see all the
frequencies of the interfering interference (possibly with "mirror frequencies" if
interference is above 1 MHz), which means that you have a tool in your hands to find the
Summary of Contents for ADC Series
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