High Resistance Indicator - del50004
Measuring Tera Ohms and Giga Ohms needs 100V and
above for good measurement. This circuit can measure
or indicate the rough magnitude of the resistor.
100, 10 or 1 Mega Ohms.
When 10V is applied on a resistor like 1 Mega Ohms.
The currnet is 10 Micro Amp. 10 Mega gives One
microamp. If this goes away in the bias and leakage
of the circuit. There is no measurement. We need to
use FET input Amps. The bias current can cause an
error too. Offset voltages also need to be low.
Description - I don't remember if this circuit
worked properly. But a few were made and i might not
have shown the modifications that were done to make
it work. This was meant to be a portable, low
cost, insulation tester for an electrician. If you
try it out and debug it it may work well.
resistance & capacitance without A/D
A negative voltage is derived by shifting gnd with
two diodes, i feel this did not work very well. Two
pins of CD4028 pins are also used to boost the
reference to get two extra ranges as 4051 has a 100E
Theory of Operation -The 555 clock makes 4029
counter count. But the clock can be clamped to gnd
by a TL062 window comparator. The clock is frozen
when the input value to comparator pin 5-2 is within
a lower limit and upper limit "window" pin 3-6.
The 4029 counter BCD is decoded to decimal by 4028
which drives the LEDs, keep LED drive within 3mA or
chip will be loaded. Use high efficiency
Meter with LED Analog Bar
The 4029 BCD also controls a shunt resistor array
with CMOS switches 4051. The voltage across shunt is
a sample of leakage current. This is compared in the
window comparator to freeze the Clock and LED
display to give a reading of the leakage current or
Here is a professional instrument - High
Resistance Meter - Model HR2 - The Model HR2
meter measures resistance in nine ranges from 1 ohm
to 1.9999 Tera ohms (1.9999x1012 ohms), and
conductance in a single range of 0.00 to 199.99 pS.