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5790A
Operators Manual
If you change the input voltage slightly with the filter active, you will not
get correct readings until the filter has been completely flushed. With the
RESTART threshold set to coarse and a small input change, the "U"
annunciator may not light. You can manually restart the filter by pressing
[TRIG].
4-19. Hi Res Softkey
The "Hi Res" softkey in the Measurement Control menu increases Measurement Display
resolution exactly like setting the Digital Filter to SLOW or MEDIUM. Refer to Table 4-
5 for the effect of this softkey.
4-20. Selecting Auto or Locked Range
When set to autorange, the 5790A ranges up or down and usually selects the best range in
which to measure a voltage. However, for measurements near full-scale, you may need to
lock the range to keep the 5790A in the desired range. Autorange is selected at power-up
and after a RESET. The setting of AUTO or LOCKED range is indicated under the range
value on the left side of the Control Display as shown below:
To lock the 5790A range press the "Range" softkey and note that the label changes to
"LOCKED." You can also lock a range by simply pressing one of the range select keys.
All further measurements are taken in the locked range until the range is reset to AUTO.
Locking a range and applying excessive voltage for that range does not damage the
instrument if voltage and current limits are observed (1000 V dc or rms, and 200 mA
max).
The 5790A input impedance is dependent on the range selected. For low voltage ranges,
2.2V and below, the 5790A has a high input impedance minimizing errors associated
with sources with higher impedances (such as the 5700A millivolt ranges which are 50
ohms). For the 5790A higher voltage ranges, input impedances as low as 50 kΩ are
obtained. A temporary introduction of a 50 kΩ load (which will occur during 5790A
auto-range) may affect a source instrument. If the output voltage of a source instrument is
affected more than 10 %, resulting from 5790A auto-ranging, the 5790A will follow the
source voltage fluctuations. Because of the continual voltage fluctuations between the
range changes, a condition may arise where the instruments are not able to settle to a
stable state.
The 5205A and 5215A instruments provide an internal slew rate trip mechanism that is
affected by load fluctuations that occur during voltage transitions. The 5205A and 5215A
instruments expect their loads to be stable during voltage transitions. If the load voltage is
not stable, a slew rate trip condition may occur. If the slew rate monitor is triggered, the
5205A and 5215A will momentarily source a low voltage and will try to apply the
desired voltage again. As a result, a cyclic pattern occurs and the 5790A auto-ranging
4-14
Note
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