4-2
Figure 4.1 shows how the relay is arranged. Figure 4.2 shows the construction
details. The gold fingers attached to the relay armature make contact to gold pads on printed
circuit boards. A permanent ceramic magnet holds the armature in place against one of the two
pole pieces. If the coil on the side opposite is energized, the armature will toggle so that it is
held against the other pole piece. once the armature has toggled the current in the coil can be
removed. This requires less than ten milliseconds.
The relays used in the scanner have 3-pole, 2-throw bifurcated contacts. The contacts
short out parallel traces on the printed circuit board connecting the channel inputs to the output
lines. A third contact provides current to a light on the front panel to indicate which relay is
closed.
4.2 LOW THERMAL DESIGN
Special care has been taken to minimize thermal offsets. The switches used are latching
relays requiring only a short pulse to actuate, and thus no self-heating occurs. Gold plated
fingers on the relay armature make direct contact to hard gold pads on special circuit boards.
Relays make connection by shorting together adjacent pads on the board with pairs of
contacts. Thus any thermal emf caused by a contact is canceled out by the nearly equal thermal
emf generated by the other half of the pair.
Switching assemblies with eight relays to a PC board are housed in a heavy machined
aluminum box. This isothermal enclosure helps to maintain a uniform temperature at each of
the relay contacts.
FIGURE 4.3 SCANNER CONFIGUATION
The printed circuit edge connectors carry only the relay coil and panel light circuits. All
the channel input lines are soldered to the relay boards directly to prevent the thermal and noise
voltages caused by connectors.
VOLTMETER
LOW LINES
UP TO 16 OR 32
VOLTAGE
STANDARDS
B LINES
A LINES
Summary of Contents for 160A
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