The optional FTB-620ES's on-board milliam-
meter provides an independent verification of
the AMPTEC 620ES's output current levels are
less than 10 mA. The 620ES failsafe current
circuitry limits the 620ES such that
one should
never see a current level
of 15.0 mA or higher.
With one test lead (i.e. red ring tipped banana )
plugged into the meter panel jack and the other
test lead (i.e. black ring tipped banana jack)
plugged into the common panel jack, the
milliammeter will display the actual test current
coming from the 620ES Igniter Tester, when the
test leads are connected and the 620ES is in
operation mode. The span of the DC
milliammeter is 0 to 10 milliamperes full-scale.
If the test leads are connected backwards to the
620ES DC milliammeter being DC based will
not measure.
The test resistors of the FTB-620ES may also
be used to verify general 620ES operation and
functionality.
Keep in mind the proper resis-
tance range should be selected in order to mea-
sure a selected test resistor. You can’t measure a
1000 ohm resistor on the 200 ohm range of the
620ES. With one test lead (i.e. red banana lead )
plugged into the selected test resistor panel jack
and the other test lead (i.e. black banana lead)
plugged into the common panel jack, the 620ES
Igniter Tester should display a resistance value
close to the labeled value of the resistor. The
0.1 ohm resistor is commonly used to test the
bottom or low end
(i.e. linearity) of a given 620ES resistance
range. The 0.1 ohm resistor can be used to
check the 620ES’s zero offset.
Refer the AMPTEC 620ES to qualified service
personnel (i.e Calibration Lab) if you suspect
(i.e large error) the 620ES measurement display
readings don’t agree with the resistor values
labeled on 620ES Function Test Section. Do not
attempt to repair the 620ES unless you are
qualified.
D-3. 4-Wire Resistance Measurement
The four-terminal configuration of the 620ES
eliminates measurement errors normally caused
by "
in series
" test lead resistance and "
contact
"
resistance.
In many resistance measurement applications the
contact resistance and can exceed the value of
the test resistance by several orders of magni-
tude. The AMPTEC 620ES overcomes this
potential error source by providing two terminals
of constant current (
I
high and
I
low) and an
additional two terminals for high impedance
voltage measurement. The constant current
source uses a variable compliance voltage circuit
to overcome lead and contact resistance until the
current loop is a constant level. The result is a
fast, accurate resistance measurement of the test
resistance, independent of the resistance of the
current carrying leads.
Figure D-1 above illustrates the 4-wire principle
eliminates lead, wire and contact resistances as
potential error sources. The internal constant
current source inherently overcomes all series
resistance (within compliance voltage limits) and
delivers a precise constant current.
Separate DC
to DC isolation circuitry provides independent
circuit voltage supplies for both polarities of
the constant current source circuit
. The internal
high-impedance Digital Voltmeter (DVM)
senses the voltage drop across the test resistance
(i.e. squib or detonator). There is negligible
contact and lead resistance error created by the
voltage measurement because the high input
impedance of the DVM limits current flow in the
voltage (V
hi
and V
low
) leads.
D-4.
Connections
Connections are made to the front panel termi-
nals using a 4-wire configuration as described in
section D-3.
IGNITER TESTER
Figure D1 - Igniter Tester Kelvin Block Diagram
* contact resistance
*
*
IGNITER
LEAD RESISTANCE
LEAD RESISTANCE
P
O
O
L
T
N
E
R
R
U
C
DC to DC ISOLA
TOR
HIGH IMPEDANCE
VOL
TMETER
4.8 VDC BA
TTER
Y
DC to DC ISOLA
T
OR
COMPLIANC
VOLTAGE
LIMITED
CONSTANT
CURRENT
SOURCE
E
