E-5.2 AMPTEC 601ES Resistance
E-5.5 MICROPROCESSOR
E-5.6 DIGITAL VOLT METER
The AMPTEC 601ES
resistance measurement function works using the principle of OHM'S LAW
(V/I=R). It outputs a constant DC current through the unknown resistance then measures the voltage drop
across the resistance. The
measurement circuit then scales magnitude and displays the V/I ratio
as resistance. For example, the 2 Ohm range outputs a constant 5.0 mA
. When 5.0 mA passes through a
1.0 Ohm resistor the result is a 5.0 mV drop. We then route the measured voltage drop (i.e. 5.0 mV) into the
and get 50.0 mV, which is routed into the DVM chip (MAX7129) which drives the
LCD display as 1.0000 Ohm. The 20 Ohm range also outputs 5mA of constant failsafe current. When 5 mA
is routed through a 10 ohm resister, you get 50mV.
10.000 Ohms. The 200 Ohm range outputs 500uA. Put that across a 100
Ohm resister and you get 50mV which put into the
displays
100.00 Ohms. As
the range resistance goes up by a factor of 10. The
current goes down by a factor of 10 keeping the
voltage at 50mV.
IC101 is a 5 volt regulator with an enable pin 4. Pin 4 normally sits at +5V through RN101:3 and RN101:1.
When the Power switch is pressed SW101 pin 4 is pulled to ground through D101, and +5 is turned on
which then goes to IC102 a 5 volt regulator. Once the power is turned on the microprocessor wakes up and
turns on TR101, which then holds pin 4 low keeping the power on. Even when the momentary power switch
is released. When the power switch is pressed again to turn the unit off TR102 is turned on and a signal is
sent to the micro processor and it turns off TR101 which allows pin 4 to go high and turns the power off.
The micro can also turn the unit off the same way after a certain time period has elapsed. This is to save
battery life See FIG. H-1.
The micro can turn on TR201-TR209 using IC201 and I 202. These fets are used to set and reset latching
relays on the current board.
DMM
601ES ohms
DC
which is also routed into the DVM chip (MAX7129)
which drives the LCD display as
DVM chip (MAX7129)
it as
DC
C
The connection is made through three ribbon connectors J201, J202, J203. A
signal also comes back through these connectors indicating which relay is on and this is used to control the
decimal point and K on the display. See FIG. H-2.
IC301 is the microprocessor it can be programed through P301 when JP301 is in the P position and operate
when JP301 is in the N position. J302 comes from the front panel range switch to let the micro know which
range has been selected. It then sends the necessary signal to IC201 and IC202 on sheet 2 to select the
proper FET to turn on the range relay on the current board. JP303 is used to tell the micro which time delay
is selected to automatically turn the unit off. It uses PTC1 to turn the power on and off and PTD7 to detect
if the power switch was pressed. These lines go to sheet 1. Ic302 is used to tell if it safe to change ranges.
See FIG. H-3.
IC402 is an X 10 Amplifier used for the 2 Ohm range. RL401 is used to switch the amplifier in and out.
D401 is the reference Zener. RV401 is used to set the reference voltage to 500 milli volts. In the 100 mV
measurement mode 50 mV in will display 10000. RL402 is used to switch in an offset in conjunction with
the front panel zero pot for the 2 and 20 Ohm ranges. RL403 is used for the 200 Ohm range. Above 200
Ohms on offset is used. P401 is used to send the display information to the front panel LCD display. See
FIG. H-4
x10 Amplifier circuit
E-5.3 POWER SUPPLY
E-5.4 RELAY CONTROL
.
Sect. E - General Operation and Design
18
