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2-12 Agilent 87130A Operating and Service Manual
Installing the 87130A Attenuator/Switch Driver
Connecting Switch Drivers to Switches and Attenuators
70611-60011, and 70612-60011 cables of #28 AWG wire size, at a total
cable length of 32.8 feet from the 87130A would have a voltage of 20.3 volts
available at the driver board. (21.5 V - (750 mA X 0.065 ohms per foot X
32.8 feet X 0.75)).*
This leaves 0.3 V that can be dropped in the wires from the board to the
switches. Thus, if each switch has 400 mA actuating plus 50 mA quiescent
current, a combined length of 16.6 feet of #26 AWG wire would be the
maximum length permissible to meet switch specifications. (450 mA X 0.04
ohms per foot X 16.6 feet = 0.3 V) Any LED current must also be added to
these calculations.
Special longer lengths of heavier-gauge driver (68 pin) and CPU (36 pin)
cables are available. Refer to “Service and Support” on page v for ordering
information.
* This calculation makes two assumptions:
(1) There are no other devices which consume quiescent current
connected to the driver boards between the 87130A and the
seventh driver board.
(2) The factor 0.75 in this equation is used to calculate an “equivalent”
cable length for forward and return path since there are two + 24 V
lines in parallel and 4 return lines in parallel.