Amptec Research 620VN Operation & Maintenance Manual Download

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Jacks. All AMPTEC 620VN Kelvin leads have
the 4 wire current high, current low as well as
the voltage sense high and voltage sense low
routed to the end of the leads. The 4 wire Kelvin
wires then terminate in a pair of gold plated clip
jaws (upper and lower jaws). One Kelvin Clip
for current and voltage high, and another Kelvin
Clip for current and voltage low.

For 620 series test leads other than those termi-
nated with banana plugs, RG-58 Shielded Coax
Cabling is recommended. Customer built test
wiring should maintaining the four wire Kelvin
measurement if possible. Make the current
conductor the largest conductor and keep the
voltage sense input shielded or inside the cur-
rent shield. The AMPTEC 620 series Igniter
Tester's five way input jacks allow for custom-
ized wire connections, extended kelvin wiring
(beyond 100 feet depending upon conductor
gauge), cables terminated with spade lugs, and
special banana jacks can all be used with the
AMPTEC 620 Tester.

All AMPTEC ohmmeters use a high impedance
voltmeter as part of the resistance measurement
process. This voltmeter is a highly accurate and
stable 4½ digit analog-to-digital converter (A to
D). The high impedance DVM must receive a
voltage drop in order to display the proper
value. When the DVM is not receiving a defi-
nite input signal, the output reading from the
Analog to Digital Convertor can appear random
and wandering. The display may indicate a
randomly wandering number or it may indicate
an overrange (flashing) condition. This unpre-
dictable display (No input to the DVM) condi-
tion is not a malfunction, in fact, just a charac-
teristic of the high impedance voltmeter circuit
and

should not be mistaken for a fault in the

instrument

- As this condition is simply a state

of an “open circuit” or “nothing connected” to
the DVM circuitry. A flashing display (on and
off usually all zeros) indicates an over-range
condition whenever the test lead terminals are
open, or the resistance under test is a higher
value than the range selected on the AMPTEC
620 tester.

Connecting V

to I

and V

to I

eliminates the wandering (open circuit) display
condition

Figure D-1 above illustrates the 4-wire princi-
ple 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 inde-
pendent circuit voltage supplies for both polar-
ities 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

and V

low

) leads.

D-5.

Connections

Connections should be made to the front and
rear panel terminals using a 4-wire configura-
tion as described in section D-3. Next connect
the 4 wire Kelvin (Option "300") Clip Test
Leads into the AMPTEC 620 Igniter Tester .
The AMPTEC 620 front panel input jacks are
spaced to only allow horizontal access (i.e.

high and

high) if using dual banana

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 620VN overcomes this
potential error source by providing two termi-
nals of constant current (

high and

low) and

an additional two terminals for high impedance
voltage measurement. The constant current
source uses a variable compliance voltage cir-
cuit 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 resis-
tance of the current carrying leads.

IGNITER TESTER

Figure D1 - Igniter Tester Kelvin Block Diagram

* contact resistance

IGNITER

LEAD RESISTANCE