DA1855A Differential Amplifier
3-10
ISSUED: July 2002
DA1855A-OM-E Rev A
usage, the instrument may be left plugged in at all times and the
power switch left in the
1
(ON) position.
Power up indication
Upon turn-on, the model number and firmware version are briefly
displayed in the PVG readout. For example, 1855.12 indicates
that the instrument is a model DA1855A and the firmware version
is 1.2.
Precision Voltage Generator Offset Voltage
The rear panel
OFFSET VOLTAGE
BNC (PVG) output
connector, is a monitor of the Precision Voltage Generator (PVG).
The voltage present on this connector is the same voltage as that
applied to the –
INPUT
when the –
INPUT
coupling is set to
V
COMP
or internally to the DA1855A when
V
DIFF
is selected. The
OFFSET VOLTAGE
output can be used to monitor the PVG with
a digital Voltmeter (DVM). A low pass filter between the PVG
output and the –
INPUT
removes radio frequency interference
(RFI) from the signal. This filter does not attenuate the PVG
signal.
The PVG output is not attenuated by the input attenuator or
probes, whereas the input signal is. Therefore the effective range
of
V
COMP
is increased by a factor of 10 when the
÷÷
10
ATTENUATOR
is selected or a
÷
10 attenuating probe is used to
attenuate the input signal. The PVG numerical display reflects the
attenuator setting and probe attenuation when the probe is
readout encoded. As an example, if there are no probes
attached, the
÷÷
10 ATTENUATOR
is selected and the display is
set to read –155.000, the
PVG output will actually be –15.5 Volt.
The decimal in the display will be in the correct location to
indicate the voltage at the PVG output when no probes are
attached and
÷÷
1 ATTENUATOR
and
X1
GAIN
are selected.
The
OFFSET VOLTAGE
BNC (PVG) output also presents the
same voltage used internally for differential offset when
V
DIFF
is
selected. Because the PVG is applied to the amplifier to create a
true differential offset, the relationship between
V
DIFF
and the
voltage at the
OFFSET VOLTAGE
BNC (PVG) output (changes
with the amplifier gain selection according to the following table:
The maximum
V
DIFF
is multiplied by any probe attenuation
factor.The DA1855A front panel displays the correct offset
referred to the instrument input.
