Lesson 3/Learning Event 7
Figure 3-16.
Isolation Relay Chassis, Front Panel View.
(1) The SEND BIAS and REC BIAS controls adjust the current through the
bias windings of the two relays. Bias current, measured in jacks marked
SEND BIAS and REC BIAS, is initially adjusted to one-half the line (loop)
current.
For example, if line (loop) current is 60 ma, bias current
should be adjusted to 30 ma. Some correction of transitions to overcome
the effect of telegraph distortion is possible by varying bias current.
(2) The SEND LOOP and REC LOOP controls adjust the line (loop) current
to the value needed for normal operation. Line (loop) current is measured
in the jacks marked SEND LOOP and RECEIVE LOOP.
(3) All jacks on the relay chassis are series normal-through.
The
RECEIVE LOOP and SEND LOOP jacks are very convenient places to measure
telegraph transmission.
Distortion measured in the RECEIVE LOOP jack
reflects overall circuit distortion, while that in the SEND LOOP jack
reflects the amount in the sending loop only.
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