The 630ES Tester measurement circuitry is also
failsafe current limited, even under worst case
component failure.
A simple startup test
procedure which also has the 630 Tester user
perform a functional check using the
milliammeter would also detect any current
level even getting close to the Failsafe level.
For the 630ES Tester the normal or typical
operating current level is less than 5 mA, and
<10mA on most 20 ohm range versions as a
Failsafe Level
.
E-7A . Ultra-Safe Power Supply Scheme
The +5 volt power supply is provided directly
by the batteries (for driving the LED displays
and digital logic). The ±5VD is used for driving
IC8, the low battery detection circuit. The ±15V
power supply is generated by IC7 for the digital
voltmeter (DVM) chip set (IC1 and IC2).
The ±5 VA is developed by one DC to DC
convertor circuitry: composed of Q103,Q104,
T102, D103, D104, IC102 for the negative
polarity. The other DC/DC convertor is
composed is composed of Q101, Q102, T101,
D101, D102 and IC101 for the positive polarity.
R212
100K
R213
100K
R222
100K
R221
100K
R215
100K
RANGE
ATTENUATION
RESISTOR
RL
I hi
I Lo
IC201
IC202
Figure E-3 Constant Current Circuit
