Teledyne LeCroy DA1855A - Manual (Page 42)

DA1855A Differential Amplifier
36 922258-00 Rev A
The maximum common mode range is ± 15.5 Volt when a signal is applied directly (÷1 ATTENUATOR
and no probes) to theDA1855A's + and – INPUTs.
Attenuating the input signal extends the common mode range by the same factor as the
attenuation. Pressing the ÷10 ATTENUATOR button increases the common mode range to±155 Volt,
and using a probe with a ÷10 attenuation factor will too. The effect of the internal ÷10 ATTENUATOR
and the attenuation factor of probes is multiplied just as the signal is attenuated. As an example,
using the amplifier’s ÷10
ATTENUATOR with a probe having a ÷100 attenuation factor (total attenuation of ÷1000) results in a
common mode range of15, 500 Volt. In this case, the probe’s maximum voltage rating probably
limits the maximum common mode input voltage.
The gain setting of the amplifier has no effect on common mode range; it is the same in X10 GAIN as
it is in X1.
When making measurements on circuits that are power line referenced, be sure to use enough total
attenuation to keep the peak voltage at the amplifier input below 15.5 Volt. The power line voltage
in North America and Japan can exceed 170 V pand therefore at least a total attenuation of ÷100
should be used. Line voltages in some other countries are larger but their peak voltages do not
exceed the 1550 Volt common mode range that a ÷100 attenuation factor provides.
Using the Oscilloscope POSITION control
(D OES NOT APPLY WHEN USING A T ELEDYNE L E C ROY OSCILLOSCOPE WITH P RO B US INTERFACE )
When operating the DA1855A with a scope, it is very important to set the oscilloscope’s position
and/or offset control to center screen, for several reasons.
First, the linear portion of the DA1855A's ± 500 mV output range is centered around zero volts. As
the DA1855A begins to exceed its limits, the output signal will be distorted. Moving the
oscilloscope’s position control way from center screen can allow these distortions to appear on the
oscilloscope’s screen where they may be mistaken for part of the displayed signal.
Second, proper operation of the DA1855A's Precision Voltage Generator (PVG) depends on the
operator knowing the location of zero volts on the display. The readout in the PVG is designed to
display the voltage of the signal as it crosses the centerline of the oscilloscope screen. If the
oscilloscope’s position or offset control has been moved, incorrect readings could result.
Using scale factors greater than 100 mV/Div
(D OES NOT APPLY WHEN USING A T ELEDYNE L E C ROY OSCILLOSCOPE WITH P RO B US INTERFACE )
“I know the input to the DA1855A is a sine wave, but I am seeing a square wave on the
oscilloscope.” This comment is the result of setting the oscilloscope Volt/Div to something greater
than 100 mV/div. If the oscilloscope sensitivity is set to 200mV/div, the DA1855A will limit at 2½
divisions above and below center screen (zero volt point if the oscilloscope’s position control is