source resistance on direct current and minimizes input current effect (p.
) on ADC input
zero offset voltage. We can state, that: ADC input of
E20-10
of revision А is incompatible with
signal source with resistance of more than 10 kOhm on direct current.
For E20-10 of revision
В under same case the minimization of input offset voltage for ADC
input can be achieved by software disconnecting of offset input current and, in this case, conceptual
restrictions of revision A are ended.
Please note, that in all revisions of
E20-10
it will be preferable to have signal source low
resistance to optimize signal-to-noise ratio
6.5.4.3.
On sta ndard feeler oscillographic gauge
connectivity
ADC input BNC connectors of
E20-10
suggest the users on standard feeler gauge
connectivity to divider 1:1/1:10 rated at oscillograph input resistance of 1 MOhm and input
capacitance of 15-30 pF. It should be noted, that such gauge on direct current under mode
1:10
in
relation to ADC input is equivalent to high-resistance signal source (more than 10 kOhm) and with
E20-10
of revision A such
gauge under mode of 1:10 is incompatible with E20-10
revision А
(p.
), but compatible with
E20-10
or revision В, if input current will be off in software (input
current is disconnected "by default" in revision В). It is required to match the gauge. Con
sider these
issues in details.
Standard feeler oscillographic gauge is, generally, rated at oscillograph input resistance of 1
MOhm. Under mode of 1:10 the device input resistance serves as gauge voltage divider "lower
arm" of 1:10, while the gauge transfer impedance (about 9 MOhm) serves as divider "upper arm".
So, to provide dividing function 1:10 if oscillograph gauge it is required to have connecting in
parallel to input E20-10 of resistor of 1.1 MOhm
. This resistor connected in parallel to input
resistance E20-10 will provide required 1 MOhm cumulatively for standard feeler oscillographic
gauge load.
We can assume
,
that in mode 1: 1 the standard gauge of the oscilloscope is rather well
matched in frequency band up to 5 MHz with ADV input of
E20-10
of any revision, since in 1: 1
DC mode the through resistance of the gauge is not too high, and the inconsistency in alternating
current affects the higher frequencies that do not fall within the bandwidth of the ADC input. In this
case, input current curtailability in
E20-10
of revision B provides the gauge connectivity 1: 1 to
high-impedance signal sources, as in the case of a conventional oscilloscope.
Gauge accurate matching across the alternating current in 1:10 mode can be performed with
operating tuning condenser located on the gauge BNC connector, if, of course, your gauge has such
a tuning.
The parallel connection to E20-
10 input of a 1.1 MΩ resistor, as was recommended above,
can technically be done by switching the oscilloscope gauge via BNC load adapter
.
6.5.4.4.
On effect of through currents on signal-to-noise
ratio
ADC input of
E20-10
has bipolar, single-phase voltage input without galvanic isolation (see
input types classification in 2).
19
This adapter is not delivered by L-card. When necessary L-Card is ready to consider the possibility of E20-10
modification release with input resis
tance of 1 MΩ. If you are interested in such E20
-10 modification, please contact the
