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Detailed Description

Analog Section

Figures E2 diagrams A thru D shows the 
equivalent circuit of the analog section in 3 
different phases of operation. The system will 
perform conversions at a rate determined by the 
clock frequency 40,002 clock periods per cycle. 
(see Figure E1B shown earlier in this chapter for 
details of conversion timing).

Auto-Zero Phase I (Figure E2A) 

During the Auto-Zero, the input of the buffer is 
connected to V REF through switch 2, and 
switch 3 closes a loop around the integrator and 
comparator, the purpose of which is to charge 
the Auto-Zero capacitor until the integrator 
output dose not change with time. Also, 
switches 1 and 2 recharge the reference 
capacitor to V REF.

Input Integrate Phase II (Figure E2B)

During Input Integrate the Auto-Zero loop is 
opened and the Analog Input is connected to the 
Buffer Input through switch 4 and C REF if the 
input signal is zero, the buffer, integrator and 
comparator will see the same voltage that 
existed in the previous state (Auto-Zero). Thus, 
the integrator output will not change but will 
remain stationary during the entire input 
integrate cycle. If V 

IN

 is not equal to zero, and 

an umbalanced condition exists compared to the 
Auto-Zero Phase, the integrator will generate a 
ramp whose slope is proportional to V 

IN

.

Deintegrate Phase II (Figures E2C and 
Figures E2D)

During the Deintegrate phase, switch 5 is closed 
and a voltage which is V REF more positive 
than during Auto-Zero is impressed on the 
BUFFER INPUT. Thus the referance capacitor 
stores the equivalent voltage. This returns the 
output of the integrator to the zero crossing 
point established in Phase I. The time, or 
number of counts, required to do this is 
proportional to the input voltage.

E-4-1. Reference Voltage

The precision reference voltage required to do 
the A/D conversion is developed by IC201.  The 
zener voltage is attenuated to approximately -
0.5V .  This voltage is applied to IC2-7 . 

E-4-2. LED Display

The output format from IC2 is in Binary Coded 
Decimal (BCD) format. Each digit is scanned 
for 10 clock pulses. The scan sequence is D5 D4 
D3 D2 D1. This drives Q1 thru Q5, which in 
turn drivers the seven segment displays. The 
BCD data is converted to seven segment format 
by IC4. When the 620A-4R electronics are in 
open circuit or over-range mode the display 
flashes “

0000"

. IC5 is a 1 MHz oscillator 

which is divided by 10 by IC6. The 100 KHz 
clock output  then goes to IC2.

E-5.

Ohms-To-DC Converter

The ohms-to-DC converter generates a constant 
current which is passed through the device under 
test to develop the voltage measured by the A/D 
converter.

E-5-1. Constant Current Source

The constant current source is composed of 
IC201, IC202, Q202, D203  and their associated 
components.  The input to the constant current 
source is approxi1.05 volts, developed 
at IC201-7 and connected to IC201-13 through 
R209 and R210. The heart of the constant 
current source is the voltage-to-current 
converter.  A simplified schematic of this circuit 
is shown in Figure E-4 and described in Section 
E-5-2.  The amplifier of IC201-12 is an invertor, 
and its output is applied to IC201-9.  The 
amplifier of IC201-8 has unity gain due to the 
feedback through R213  .  Its output is applied 
to the inverting input of IC202-3.  The output of  
IC202-6 provides feedback to the non-inverting 
input of IC201-10.  This circuit operates to 
maintain the inverting input at IC202-3 and the 
non-inverting input at IC202-2 at the same 
potential.

Summary of Contents for 620A 4R

Page 1: ...AUSTIN TEXAS 78737 USA CAGE CODE 1CRL2 PHONE 512 858 4045 or 1 800 350 5105 from the USA e mail info amptec com FAX 512 858 4340 or 1 800 430 5440 from the USA website http www amptec com 620A 4R Batt...

Page 2: ...ARRANTY ________________________________________________________ Permission and a return authorization RMA number must be obtained directly from AMPTEC s customer service department via phone FAX or e...

Page 3: ...Charger Power Requirements A 5 Setup and Use CHAPTER B 620A 4R FAILSAFE OHMMETER SPECIFICATIONS Table B 2 Specifications CHAPTER C REPLACEMENT OPTIONAL ANDACCESSORYITEMS C 1 Available Accessories and...

Page 4: ...ER F ROUTINE MAINTENANCE F 1 General F 2 Required Test Equipment F 3 Calibration Procedure F 4 Battery Replacement Instructions CHAPTER G COMPONENT PARTS LISTS 620 400 Parts Assembly list CHAPTER H SC...

Page 5: ...eable batteries reach a low charge level a negative sign will appear on the display The 620A 4R has a battery monitoring circuit that indicates it is time to plug in the battery charger A 2 Receiving...

Page 6: ...d is open The 620A 4R has a way to remove it s lid completely for example when used in an indoor laboratory environment With the 620A 4R open remove the units two hinge pins hex type by twisting them...

Page 7: ...entioned earlier of course the AC DC Battery Charger must be plugged into the 620A 4R s notched connector to facilitate charging the batteries Although the batteries are fully charged prior to shipmen...

Page 8: ...d 35 C 50 C Instrument Display 20 000 count 4 digit Super Bright Light Emitting Diodes LED Over Range Indication select next higher range 620A 4R Display flashes Measurement Update Rate Approximately...

Page 9: ...er that verifies each individual replacement battery voltage charge level inspector signature along with the inspection date CHAPTER C REPLACEMENT OPTIONALAND ACCESSORY ITEMS 3 2 Test Lead Sets and Pr...

Page 10: ...Terminal Kelvin Mini probes photo shown above Each probe has two spring loaded gold plated steel tips with 0 18 separation one red and one black handheld probe Excellent general purpose 4 Wire Kelvin...

Page 11: ...anana leads which provide a 4 wire Kelvin connection from the adapter to the 620A Ohmmeter No lead resistance errors In some applications i e AIM 7 Missile harnesses regular alligator clip leads canno...

Page 12: ...s just below the display on the left see item 11 of the 620A 4R Front Panel Diagram When a given range is selected an indicator LED informs the user Also note that a resistance range must be selected...

Page 13: ...rews have been removed for calibration access 4 Test Lead Connection Panel Jacks The 48 long dual banana Alligator Test Leads plug directly into the Voltage High and Voltage low and Current high and C...

Page 14: ...item 7 of the 620A 4R Diagram The fuse protects internal batteries from excessive charging currents Replace blown fuses with the same type and rating only The Charging System The slimline AC to DC bat...

Page 15: ...shielded In addition custom probes and test lead sets are optionally available for customized wiring connections kelvin clips cables terminated with spade lugs and special banana jacks All AMPTEC ohm...

Page 16: ...512 447 7456 International Overseas or FAX 512 447 7455 email service amptec com D 7 Failsafe Operation The AMPTEC 620 Series of Igniter Testers or failsafe ohmmeters incorporate a constant current s...

Page 17: ...50 VDC To make this adjustment first remove the fuse from the fuseholder With an adjustable DC power supply set the power supply output to be 4 50 VDC Be sure to observe power supply polarity Connect...

Page 18: ...cate the batteries need charging or fuse needs replacing If the 620A 4R exhibits problems that cannot be eliminated by reviewing Chapters B and D the following guidelines have been established to help...

Page 19: ...or move the replacement part until the solder has cooled Cold solder and bad solder joints can cause more problems Use the chassis ground connect to the common terminal of the functional test section...

Page 20: ...the analog part and the ICL71C03 takes care of the digital part of the 4 digit 20 000 count dual slope conversion COUNTERS DISPLAY COMPARATOR BUFFER MULTIPLEXER ZERO CROSSING DETECTOR INTEG UUT CONTRO...

Page 21: ...EGRATOR INTEGRATOR COMPARATOR COMPARATOR CAZ CAZ CSTRAY CSTRAY RINT RINT FIGURE E 2B PHASE ll INTEGRATE INPUT FIGURE E 2C PHASE lll AND DE INTEGRATE CINT CINT VIN VIN CREF CREF 3 3 1 1 2 2 6 6 5 5 4 4...

Page 22: ...shed in Phase I The time or number of counts required to do this is proportional to the input voltage E 4 1 Reference Voltage The precision reference voltage required to do the A D conversion is devel...

Page 23: ...t as it was when the output terminals were shorted The current through R is 10 L milliamperes just as it was through the jumper when the output terminals were shorted E 6 Failsafe Design Reference to...

Page 24: ...wer 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...

Page 25: ...range push buttons covered by silicone rubber boots and their corresponding panel mount LEDS IC 2 is a latch that will latch its output to the corresponding range push button input Its output turns o...

Page 26: ...AMPTEC 620 package may have too much resistance offset for the actual calibration of 620 Igniter Testers versions fitted with a low 2 0 Ohm range Contact AMPTEC for information on the 305 48 long 4 w...

Page 27: ...n Return the calibration access screws to the perimeter of the 620 main top panel 2 Adjust RV1 for a display indication of 100 00 3 Check the 2 0 KOhm range with the 1000 Ohm Standard Resistor Check t...

Page 28: ......

Page 29: ...3 D104 and D202 D201 D203 Relay Board 04 30015 1 620A Relay Board DWG 620A 702 REVB RL1 05 03006 1 Relay Aromat S2EB 5V CHG1 05 79393 1 Slimline 9 VDC Battery Charger AMPTEC Modified Volgen Model LV 1...

Page 30: ...rostat 50KW DK RV6N503C ND Allied 753 2503 HNDL1 05 77201 2 Handles Front Panel Mount Type Allied 839 9119 STF1 05 77251 2 Standoff Box of 100 Allied 839 2357 KB1 05 77311 1 Knob for shaft of the zero...

Page 31: ...ly Rev D 620 601 2 1 page 620 Display Board Assembly 620 070 3 pages 620 Ohmmeter Schematics 1 DVM1 Rev D 2 I_SRC Current Source Rev D 3 DISP Display Rev D 620 077 1 page 620 Relay PCB Schematic Rev A...

Page 32: ...bon Cable Header routes to the Top Panel D6 Q6 D7 Q7 D8 8 Q8 470W R6 470W R10 620 RELAY BOARD Drawing 620 077 Cage Code 1CRL2 RESEARCH AMPTEC Page 1 of 1 INPUTS OUTPUT OE LE D Q L H H H L H L L H X X...

Page 33: ...620 FRONT PANEL RANGE SWITCH SCHEMATIC Drawing 620 078 RESEARCH AMPTEC Page 1 of 1 Front Panel LED Indicators 2KW Range Indicator 200W Range Indicator Revision A Scale none...

Page 34: ...D1 C1 C2 D2 RV1 D3 R4 R9 R6 R14 RV201 R13 R3 R2 R1 R15 Q5 R7 C3 C5 C4 R8 IC3 C11 RV2 C12 IC4 RN1 Q4 Q3 Q2 Q1 D5 R17B C8 IC9 C10 S1 D4 R225 R224 R223B C13 RV3 P1 R20 R19 IC8 C9 R16 R18 IC10 IC11 R23 R2...

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