WPI ISO-DAM, Instruction Manual

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ISO-DAM
1. Amplifier input connections are completely disconnected from the Power (Mains)
ground.
2. No significant current can flow from the preamplifier input terminals to ground.
Therefore, input connectors are intrinsically safe and cannot cause electrical shock at the
site of measurement.
The wall power supply unit provides DC power to the post-isolation output stage of the
amplifier. The power supply also provides DC current to charge the isolated front end
batteries when the power switch is turned off. Estimated battery operating time between
charges is 160 hours. When the ISO-DAM is in use, keep the wall power (AC adapter)
plugged in in order to supply DC power to the output stage of the amplifier.
Noise and Interference
The bane of low level bioelectric recording is electrical noise and interference originating
from the current and voltage in the power mains and room lighting power. Every
high amplification preamplifier is subject to this handicap; particularly when using
microelectrodes. It is therefore recommended that all input leads be shielded and
the preparation connected to earth (ground). Often, it will be necessary to enclose
the preparation and electrode lead wires in a Faraday cage or shield to reduce mains
induction to sufficiently low levels. Often it will be beneficial to extinguish overhead
fluorescent lighting as well.
Quick Test
To determine if the preamplifier is operational, switch the Low Filter switch to GND and
the Gain switch to
×
10. With the power supply connected, the Off/Charge lamp should
be lit. Turn the Power switch to On. The On lamp should light. The two red Output lamps
should easily switch between the - and + lamps as the Zero knob is rotated.
Input Connection
The input connector of the preamplifier is a single 3-pin socket (pin 1 is positive [+],
pin 2 is negative [–], pin 3 is ground). The input plug has a shielded cable (1.5 m)
terminating in red, black, white and green wires. The red wire is positive (non-inverting);
the black wire is negative (inverting); white and green wires are not used. Ground
reference is the copper braid (pin 3). The Faraday ground socket, located to the right of
the input socket, is a 3 mm banana-type socket (one banana plug is also included with
the instrument). The user should connect this receptacle to the system ground point (
i.e.
,
that point where the recording site is connected to Power (Mains) ground. The subject or
2 WOrLD PrECISION INSTruMENTS
preparation should also be connected to ground. Input protective devices limit the input
differential signal from exceeding ± 3 volts.
DC Bal.
The DC Bal. (balance) potentiometer allows the user to adjust Gain switch position
stability. The potentiometer is accessible with a small screwdriver hole on the front
panel. To adjust the DC Bal. first perform the QuICK TEST procedure as outlined above.
using an oscilloscope or recorder connected to the Output connector, adjust the Zero
knob so that the output trace on the recorder is near the zero volt level. rotate the GAIN
selector switch from ¥10 to ¥10000. If the baseline moves, readjust the DC Balance pot
at the ¥10000 setting with a small screwdriver until the baseline returns its prior setting.
The baseline should not deflect appreciably when the GAIN switch is reduced to lower
values.
Output
The maximum Output signal from the amplifier is ± 5 volts.
Filters
ISO-DAM provides selected filtering at both the high and low ends of its frequency
spectrum. The Low Filter (“high-pass”) 3 dB cut-off points are 0.1, 1, 10 and 300 Hz,
respectively. The High Filter (“low-pass”) cut-off frequencies range from 100 Hz to 10 kHz.
For example, typical settings recommended for ECG and EEG would be Low Filter at 0.1
Hz and the High Filter at 0.1 kHz (100 Hz).
DC/DC Offset
When operating the ISO-DAM as a DC amplifier, the user may require a DC offset
potential with which to compensate any existing DC voltage from the recording site. The
DC Offset knob can provide 0 to 100 millivolts of either polarity with which to reduce
(null) the net input to zero volts. This becomes increasingly necessary if high gains are to
be used with DC amplification. The toggle switch below the DC Offset knob selects the
polarity of the offset voltage. If offset adjustment is not required, the toggle switch is kept
in the Off position.
Charge
Insure that the Nickel-Cadmium batteries are fully charged before using the amplifier.
Connect the receptacle on the top side of the ISO-DAM case to the DC wall power
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