1-21. ELECTRONIC STATION (cont)
(b) Output of the summer is integrated and used to drive a power amplifier
which regulates the power applied to emitter A.
Variations in resistance of sensor A
are applied to sensor A amplifier whose output is entered into the summer.
summer, the output of the sensor A amplifier is compared to the output of the EMITTER
TEMPERATURE SET thumbwheel switch (coming from the digital/analog converter).
(c) When the output of the integrator stabilizes (as it nears the
temperature set into the thumbwheel switch), the FLAG indicator lights, indicating
that the temperature of emitter A is within 0.02°C of the preset temperature. At the
same time, a digital flag signal is sent to the IEEE 488 bus interface.
(4) Emitters B and C.
Emitters B and C, which are physically identical, have a
1.5-inch square radiating surface, controlled in l.O°C increments, relative to the
temperature of emitter A.
(a) Emitters B and C share a single sensors B and C amplifier, summer, inte-
grator, power amplifier, and the two-digit
TEMPERATURE SET thumbwheel switch.
result, emitter C cannot function while emitter B is in operation and emitter B cannot
function when emitter C is in use.
(b) Emitters B and C are slaved to the set point temperature of emitter A.
They can only have the same temperature or a higher temperature offset relative to
Offset temperature values on the two-digit
TEMPERATURE SET thumbwheel
switch are in BCD format and pass through a digital to analog converter to the
(c) This digital to analog signal is compared to the output of the sensors B
and C amplifier and to the signal from the summer in the emitter A circuitry.
resultant signal is integrated and applied to the power amplifier to heat or cool the
thermoelectric element in the emitter.
As the thermoelectric element heats or cools,
the resistance of the sensor changes.
This changing resistance of the sensor is
applied to the sensors A and B amplifier and supplied to the summer.
488 CONTROLLER POWER SUPPLY ASSEMBLY 1A2
The 488 controller power supply assembly 1A2 (FO-4) receives data
from the computer on the IEEE 488 bus and converts this data into analog signals which
are in turn used to command the outputs of four programmable power supplies.
Data flow is asynchronous, ensuring compatibility among devices
with varying response times.
Asynchronous transmission is accomplished by means of
the three handshake lines (DAV, NRFD, and NDAC).
The state of the interface is deter-
mined by the listen mode flip flop.
If the interface listen address is received while
line ATN is low, the flip flop is set and the interface enters the listener-addressed
If the unlisten command is received while line ATN is low, the flip flop is
reset and the interface exits the listener-active state.
While the interface is in
the listener-addressed state, ASCII data received via the IEEE 488 bus is converted to
hexadecimal format by the read only memory (ROM) and passed to the backplane.