Audio; Scale Ranging; Digital Analog Converter; Meter Drive - LUDLUM MODEL 19 Manual

Model 19 MICRO R METER
Ludlum Measurements, Inc.
Technical Manual

Audio

Discriminator pulses are coupled to univibrator pin 12 of U9B. Front-panel
audio - selector controls the reset at pin 13 of U9B. When
ON OFF
from pin 10 of U9B turn on oscillator U12, which drives the can-mounted
unimorph. Speaker tone is set by R31, C14; duration by R22, C7.

Scale Ranging

Detector pulses from the discriminator are coupled to univibrator pin 5 of
U9A. For each scale, the pulse width of pin 6 of U9A is controlled by the
front-panel calibration controls and their related capacitors. This
arrangement allows the same current to be delivered to C9 in proportion to
the meter reading.

Digital Analog Converter

U5 is configured as a current mirror. For each pulse of current through R24,
an equal current is delivered to C9. This charge is drained off by R25. The
voltage across C9 is proportional to the incoming count rate.

Meter Drive

The meter is driven by the collector of Q2 coupled as a voltage follower in
conjunction with pin 1 of U10.
For the battery test, the voltage follower is bypassed and the meter
movement is directly coupled to the battery through R8.

Fast/Slow Time Constant

For slow-time constant, C17 is switched from the output of the meter drive
to parallel C9.

Low Voltage Supply

Battery voltage is coupled to U11 and associated components (a switching
regulator) to provide 5 V at pin 8 to power all circuits.

High Voltage Test

A constant current is developed by collector of Q3 in proportion to HV
signal at pin 1 of U17. U16 provides a current mirror to drive the meter
Page 7-2
Section 7
, pulses
ON
February 2012