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SGD-O User Guide
1. Check the detector signal by entering DAC 112003 at the transmitter.
If the detector is set to 9.6 Vdc on air, the value should be
approximately 6.311E4.
If the value shown is 6.542E4, the detector signal is over 10 Vdc and
the detector will not work. If the value shown is less than 6.200E4,
then the detector gain is not set correctly or the detector is
malfunctioning. Refer to
2. Remove the detector lid. Use a voltmeter to measure the voltage from
pin 1 to pin 4 of J1 on the pre-amp board. Pin 1 is the pin furthest
from the edge of the board. The reading should be approximately 30
Vdc. If it is, both the +15 Vdc and -15 Vdc are coming from the
transmitter and reaching the detector.
If the voltage is only 15 Vdc, then one of the 15 Vdc supplies is not
reaching the detector. If the voltage is zero, then neither 15 Vdc
supplies are reaching the detector. Check cabling and the output of the
transmitter VPI board.
3. Measure pin 2 to pin 3 of J1. This is the output of the detector. It
should be 9.6 Vdc with air in the pipe.
If the output is 9.6 Vdc ±3.0 volts, use the R35 potentiometer on the
pre-amp board to adjust the output to 9.6 Vdc with air in the pipe.
If the output is above 10 Vdc and will not adjust, verify the gain
jumper is on W1 and the W3 jumper is not installed. If necessary,
modify these jumpers.
With the gain jumper on W1 and W3 not installed, fill the pipe with
water and see if the voltage drops below 10 Vdc. If it does not, the pre-
amp board requires repair or replacement.
4. If the output voltage does drop below 10 Vdc when the pipe is filled
with water, then the gain is set too high. Remove the W1 jumper
completely and the gain will lower to the point that you should be able
to use R35 to adjust the output to 9.6 Vdc on a pipe full of air.
If the output voltage can be adjusted with the R35 pot, but will not
increase to the 9.6 Vdc, on a pipe full of air, then the gain is set too
low. Move the W1 jumper to W2 (keeping in mind that the center
hole is the common connection). In most cases, you should now be
able to use the R35 pot to adjust the output to 9.6 Vdc on air.
Chapter 7
to adjust the gain settings.
Thermo Fisher Scientific
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