Teledyne UA-6, Installation And Operation Manual

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UA-6 Detector
Section 4 Theory of Operation
4-4
Note
Auto Baseline repeatability varies depending on the sensitivity
range used. The following lists a few examples of Auto Base-
line repeatability.
4.2.2 Logarithmic Amplifier
This circuit consists mainly of U214 (amplifier), U216 (loga-
rithmic diodes) and Q203 (buffer). The amplifier functions as a
common mode amplifier. When both photocell signals are equal,
the output at TP208 is zero. Therefore, any system noise signals
seen by both photocells are “common moded” out and not seen on
the absorbance signal.
4.2.3 Gain Amplifiers
U213 is an adjustable amplifier used to compensate the response
of optical units. Resistors inside the optical unit increase or
decrease the gain of this amplifier to maintain the amplification
of the entire system regardless of the optical unit used. The U213
amplifier couples the absorbance signal from the logarithmic
amplifier to the absorbance amplifier.
Absorbance amplifier U202B provides the sensitivity ranges
based on the front panel switch position (S5B). 0.002 range pro-
vides a gain of 100. Gain decreases to 0.1 on the 2.0 range.
4.2.4 Noise Filtering
The noise filter (U202A) is a Bessel type time delay filter whose
output is the time average of its input. Three filter settings are
possible using S04. This filter will reduce the amount of system
noise seen by the chart recorder.<%0>
In addition to U202A, the absorbance amplifier (U202B) provides
filtering in the four most sensitive ranges. The following infor-
mation relates total system rise time in seconds per sensi-
tivity/rise time setting for a 10-90% of scale signal change.
Sensitivity Range Repeatability
0.002 ±25% of chart
0.02 ±3% of chart
0.2 ±0.2% of chart
0.5 — 2.0 Repeatable
Sensitivity Noise Filter Setting
0.5 1.5 5.0
0.002 1.6 2.4 6.1
0.005 0.8 2.0 6.0
0.01 0.58 1.8 5.8
0.02 0.52 1.7 5.7
0.05 – 2.0 0.5 1.5 5.0