Single chip checks resistance

Description: A simple tester can be utilized for routine resistance checks on production lines of relays, coils, or similar components where frequent resistance changes are not necessary. The tester is constructed around a single quad op-amp chip, the LM324. A resistor, chosen to be approximately 80 times the resistance being tested, is used alongside a 5 V supply to form the current source. The first op-amp buffers the voltage generated across the resistance under test, Rx. The second op-amp amplifies this voltage. The third and fourth op-amps compare the amplified voltage with predetermined high and low limits. These limits are set using multi-turn presets with high and low limit resistors connected in place of Rx. LED 1 (red) illuminates when the resistance is high. LED 2 (green) indicates that the resistance is within acceptable limits. LED 3 (red) signifies that the resistance is low.

The resistance tester circuit employs the LM324 quad op-amp, which consists of four independent, high-gain, frequency-compensated operational amplifiers. The circuit begins with a current source generated by a resistor connected to a 5 V supply. This resistor is strategically selected to be approximately 80 times the value of the resistance to be measured, ensuring that the circuit can effectively operate within its designed range.

The first op-amp functions as a buffer, isolating the test resistance Rx from the subsequent stages of the circuit. This buffering prevents loading effects that could alter the resistance measurement. The output from this op-amp is then fed into the second op-amp, which is configured as a non-inverting amplifier. This amplification stage is crucial for enhancing the voltage signal across Rx, making it easier to compare against the set limits.

The third and fourth op-amps are configured as comparators. They compare the amplified voltage against preset reference voltages that define the acceptable range for the resistance measurement. These reference voltages are established through multi-turn potentiometers, allowing for fine-tuning of the high and low limits. The use of potentiometers facilitates easy adjustment and calibration of the circuit to accommodate different resistance ranges.

The output of the comparators drives three LEDs, providing a visual indication of the resistance status. When the measured resistance exceeds the upper limit, LED 1 (red) lights up, signaling that the resistance is too high. Conversely, when the resistance falls below the lower limit, LED 3 (red) illuminates, indicating a low resistance condition. If the resistance is within the acceptable range, LED 2 (green) lights up, confirming that the measurement is within limits. This LED indication system allows for quick and easy assessment of the resistance status, making the tester a valuable tool for production line applications.A simple tester can be used for routine checks for resistance on production lines of relays, coils, or similar components where frequent changes in resistance to be tested are not required. The tester is built around a single quad op amp chip, the LM324. R, which is chosen to be around 80 times the resistance to be checked, and the 5 V supply form the current source.

The first op amp buffers the voltage generated across the resistance tinder test, Rx. The second op amp amplifies this voltage. The third and fourth op amps compare the amplified voltage with high and low limits. The high and low limits are set on multitum presets with high and low limit resistors connected in place of Rx. LED 1 (red) lights when the resistance is high. LED 2 (green) shows that the resistance is within limits. LED 3 (red) indicates that the resistance is low.