1-21. ELECTRONIC STATION
Refer to FO-2 for a block diagram of the electronic station. The electronic
station is described in the following order:
Control unit assembly 1A1
488 controller power supply assembly 1A2
Programmable power supply assembly 1A3
DC power supply assembly 1A4
AC control panel assembly 1A5
PMT controller 1A7
Extender assembly 1A9
Disc/tape drive assembly 1A1O
Digital computer assembly 1A11
a.1 TEMPERATURE CONTROL UNIT 1A1
The temperature control unit (FO-2.1) consists of the temperature
controller, three blackbodies (heat sources), and an ambient probe. These items
together make up an ambient range IR source system.
A blackbody contains a surface
that emits high IR radiation, the exact temperature of which is controlled by the
The temperature control unit thus provides an accurate source
of IR energy.
In addition, the temperature difference between the blackbody and some
other surface may be controlled, providing a precise energy contrast.
One of the
blackbodies, designated source A, can be controlled in two modes: absolute or
In absolute mode, the absolute temperature of the blackbody is set
directly in degrees C.
In differential mode, the temperature of the blackbody is set
relative to the ambient sensor.
The two other blackbodies, designated source-B and
source C, can be controlled in differential mode relative to source A.
B or source C can be controlled, with the other source in an unpowered idle state.
Temperatures may be set either from thumbwheel switches on the front panel, or
through the GPIB (IEEE standard 488) interface.
The absolute temperature of any
source, as well as its differential temperature, can be displayed on the front panel.
In addition, the absolute temperature of any source, as well as the differential
temperature of source A, may be read through the GPIB.
(2) Temperature Measurement.
The A/D converter measures resistances between
approximately 150 to 360 ohms with a resolution of 0.0002 ohms.
Used with a 200 ohm
platinum resistance thermometer (PRT), this allows measurement of temperatures between
-60 and +200°C with a resolution of 0.0005 degrees.
Two A/D converters are used. One
measures the ambient (reference) probe and the PRT in source B.
The other measures
the PRTs in sources A and C.
The multiplexer is operated in a temperature controlled
oven for maximum stability.
It switches control and temperature data between the
probes and the A/D converters.
(3) Temperature Control.
The temperature controller contains an analog servo
loop which controls the temperatures of the blackbodies. The microprocessor controls
the set-point of the loop.
The set-point is continually adjusted based on the
temperature measurement data available to the microprocessor.