Canon A-1 Repair Manual page 37

38
with
art
opposite polarity are sent to the integration
circuit. The output of the integrator . is integrated
with the oppo·site porarity, and it will serve · to
decrease the integrated output voltage
"EO~.
See figure 10*
As Eref. remains fixed regardless of the amount of
Ex., the intergrated values have a constant slope at
all times : As a result of the intergration, EO will
become zero (t2), and at this time the 90mparator
which is connected with the integrator detects the
zero voltage and generates the signal.
T,
E.
= -
CR
Ex
+
T • . -Erd ) =O
CR
T,
""Ca
Ex
T.
f
=
-Ere
CR
T,=--'!.L Ez
=
KEx
Erel
As the above formulas obviously tell you, T2 is
exactly proportionate to the input voltage. Namely,
the "T2" is a lapse of time from tl to t2 and that
corresponds to the brigh t ness of the subject. The
counter counts pulses of the T2 and gives the digital
number in exact proportion to the metered amount of
light. After going through this cycle, the switch
"51" again returns to "a", turning on the switches
"52" on both sides of the condenser in order to
reset the cycle and start metering the voltage .
This system has the following advantages:
A) There is no need to take into account variations
in capacitors and registors. The amount once
stored into the capacitor is discharged through
the same resistance as when being charged .
As we can only pay attention to the time it
takes, there 1s no worrying about variations in
capacitors or changes in temperature and humidity,
or deformations of parts that may occur with
aging.
B) Flicker Prevention of the Light
Fluorescent lamps and those which lights up
through AC power source has, without exception,
waves particular to the AC power source. When
immediate-response elements or displays are used,
there will be a difference in metered data
between the upper end and the lower end. This
*:
This figure is inverted when observed on an oscilloscope.