The control sensor voltage is input buffered and fed to an error
amplifier along with the opposite sign set point voltage. The error
amplifier generates a signal proportional to the gain setting. With the
addition of reset (integral), output power is controlled and applied to
the system through a twenty-five watt heater.
The microprocessor also controls the BCD and
IEEE
options. These
options remotely control the set point, gain and reset as well as indicat-
ing the display temperature.
4.3 Detailed Description
A detailed description of the operation of the DRC instrument is
outlined in the following sections. The Figures required for each sec-
tion
will
be denoted in that section.
4.3.1 Power Supplies
Please refer to Figure 6.1 (Schematic
#1)
for the following dis-
cussion. There are eight different power supplies incorporated in the
DRC-series instruments. The main power transformer,
TX1,
has split pri-
maries for 115 or 230 volt AC operation. The slide switch, S2, selects
the proper line voltage.
The first secondary is output through leads
1
and 3. This secondary
is rectified by CR1 and a floating 15 volt supply is obtained through
C1, C6, and the positive 15 volt regulator U1. This supply is used to
power the constant current sources for diodes in the case of the DRC-80C
and both diodes and platinum sensors in the case of the DRC-84C.
The second secondary, through leads 2,
4,
and
6,
is full wave bridge
rectified by CR2-5.
A
+15
volt supply is generated by C2, C7 and
a
posi-
tive 15 volt regulator
U2.
The negative 15 volt supply is generated by
C3, C8 and voltage regulator
U3.
Both these supplies are used in the
A/D and D/A converters as well as the analog section.
U7 with capacitors C10, C47, C48, and C11 generate plus and minus
8
volts
for the low voltage, low offset operational amplifiers used in the analog
sect ion.
Regulators U6 and
The third secondary is through leads
8,
10,
and
12
and is full wave
rectified by CR6-7. The five volt supply that is used by the TTL IC's
is formed by C4, C9, and a 5 volt positive voltage regulator U4. A 5
volt half wave supply for the
LED
display is provided by CR8, C5 and
the 5 volt positive regulator U5. The reason for splitting the 5 volt
supplies is to avoid the LED display from loading down the main 5 volt
supply
.
The eighth supply is used
in
the output power section and
will
be
covered there.
-39-
To Next Page
Loading...