R212
100K
R213
100K
R222
100K
R221
100K
R215
100K
RANGE
ATTENUATION
RESISTOR
RL
I hi
I Lo
E
in
Figure D-5 Constant Current Circuit
IC201
IC202
limits, because the -5 volt and +5V supplies
includes inherent current limiting. Because of the
design of both supply isolation transformers T101
and T102, the ±5 volt supplies can only deliver 20
to 25 milliamperes before the DC/DC converter
disengages, dropping the -5 volt output to zero.
620ES Failsafe Current Calculation -
Worst
Case Component Failure
Please refer to Section E for a more detailed
explanation of the failsafe current source.
D-6.
Battery Monitoring Circuitry
The 620 series igniter tester display has a ±
polarity display indicator preceding the unit’s
regular 4 ½ digit numeric display. The negative
polarity display LED is used as a Low Battery
indicator. If the low battery LED is illuminated,
620 Series Igniter Tester readings should not be
trusted. An overnight recharge should be
performed before using the 620 series igniter tester
for critical testing. The batteries are fully charged
prior to shipment, it may be desirable to refresh the
charge for 24 hours before use.
As a rule of
thumb, the 620ES requires twice as much time to
fully recharge as the amount of discharge time.
Notice for Cal Lab:
The variable trimpot RV3 is
factory adjusted to have the
low battery indicator
come on at 4.50 VDC. To make this adjustment
refer to the
Maintenance Section F
of this
manual.
V
oltage limiting diode, D203, provides a 1.6 volts
maximum across R227 (100
W
) and R223 (100
W
),
which are 200 Ohms across the Igniter Testers
output terminals.
(I
max
)
Current Maximum Calculation
1.6V/110 ohms = 0.014 Amperes (15mA) max
A simple startup test procedure which also has the
620ES Explosive Safety Tester user perform a
functional check using (optional FTB-620ES) with
AMPTEC milliammeter would also detect any
current level even getting close to the Failsafe level.
igniter could not exceed safe
Reference to the AMPTEC 620ES Igniter Tester
schematic will show that the output of IC202-6 is
actually applied to the base of transistor Q202,
which acts as a current limiter
.
The worst-case
component failure that could occur in this circuit
would be a Q202 short
, which would effectively
connect the -5 volt supply directly across R218,
D202, the range resistor and R .
L
D203, however, acts as a 1.6 volt zener diode,
limiting the voltage that can appear across the
current output terminals.
Even if every
component in the amplifier circuit shorted, the
current through the
MILLAMPERES
2
4
6
8
10
100.0 KOHM
10.0 KOHM
10.0 OHM
10.0 MOHM
620ES
Functional
Test
Box
19.0 MOHM
Functional Test Section
- The optional 620ES
Functional Test Box provides added measurement
integrity using a milliammeter and test resistors to
cross check the overall 620ES operation whenever
desired. The test resistors are for cross checking
620ES basic operation and should not be used for
calibration purposes.
Simpson
tm
DC Milliammeter
Range
- 0-10 mA
fullscale,
Accuracy
±3%
FTSR1
01-23572
0.1
W
1.0 % Wirewound
Resistor,
T
c- 25ppm/°C
FTSR2
01-23575
10.0
W <
0.1%
WirewoundResistor,
T
c- 10ppm/°C
FTSR3
01-23577
10.0 K
W
<0.1% Wirewound
Resistor,
T
c- 10ppm/°C
FTSR4
01-23583
100 K
W <
0.1% Wirewound
Resistor,
T
c- 10ppm/°C
FTSR5
01-23587
10.0 M
W <
1.0% Wirewound
Resistor,
T
c- 20ppm/°C
FTSR6
01-23589
19.0 M
W <1
.0% Wirewound
Resistor,
T
c- 50ppm/°C
