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1021 Technical Manual
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5.
C ircuit Des cription
5.1. Power Supply
The power supply circuit board is mounted on a removable bracket which runs the length of
the instrument. Eight NiMH (AA) size cells located in two plastic holders power a switch
mode regulator through a 1A fuse. The batteries may either be of the NiMH rechargeable
type (as fitted and recommended) or of the Alkaline non rechargeable type. The switch
mode regulator supplies a stab8V, a stabilised -7V and a variable stabilised 14V to
40V at 2.4W. The regulator circuitry incorporates a cut-out which operates should the
battery voltage fall below approximately 7V.
Battery life depends primarily upon the output current and voltage setting. At output
currents of less that a few mA the life of a fully charged battery should be up to 20 hours.
5.2. Mains Recharger
The mains recharger is a separate unit. It will fully charge the batteries in 12 to 16 hours.
The standard recharger requires a mains input of 200V to 240V at 50/60Hz. A recharger
requiring 100V to 120V at 50/60Hz is also available but should be specified when ordering.
The recharger is connected to the 1021 by a miniature 2 pin plug and socket shaped to
ensure correct polarity.
5.3. Circuit Module and Range Switch
The active circuitry and range switch of the 1021 are located on a printed circuit board which
is mounted on the rear of the front panel. Connection to this board is by a 9 pin connector.
The active circuitry is encapsulated and contains the precision reference circuit and output
stage. A single F250mA 20x5mm fuse that is mounted on the power supply board protects
the output.
Four trimmers for calibration are mounted on the printed circuit board (See Fig 1, page 12).