Hey guys,
At work we assemble some what we call optical sensors (consists of 2 photransistors & 1 LED), after the assembly these sensors are tested to insure that the assembly was well done.
The testing is done with an old test fixture we got many years ago from the manufacturor. (see image)
What we want is to make a new test fixture but using newer components.
We are doing this on our free time, so far this is what we got;
First we looked at what the test fixture really does, and then made a schematic.
What tester does is the following;
First you connect the sensor to the test fixture. The test box has two probes named; volts and milivolts, there you connect a multimeter.
After that is done, you have to turn the voltage adjust knob on the test box, until you read 4.5v on the multimeter connected to the volts probe.
When you have the 4.5v stabilized, you have to read the value of FC1 and FC2 (there's a switch therefore on the box) on the multimeter connected to the milivolts probe.
When these values are according to the specifications (this is done by adjusting a plate on the back of the sensor), you have turn the voltage adjust knob again until you read 0.07V or 70mV on the milivolts probe.
After this is done, you have to read the value on the volts probe, which should be around 0.15v and 0.45v.
After reading those instructions i made a simple schematic, based on what i think is going on, which is;
You use 4.5Vcc (volts probe) on the first step, then you measure the voltage across a resistor connected to each of the photransistors (FC1&FC2, what you read on the milivolts probe).
Then you lower the FC1&FC2 value till you get 0.07V, and then read the Vcc value( volts probe), which should be between 0.15 and 0.45v.
First I tested one sensor on the old test box, and got these values; FC1:3.90v, FC2:3.92v, and the last measurent (when you make the FC values 0.07v) was of 0.16v.
I build the schematic on a breadboard, and was able to get the correct values for FC1&2 (by adjusting a potmeter connected to each of the phototransistors) but when I lower the FC values to 0.07v, I get a reading on the last measurement (volts probe) of about 1.2v, which is way off.
After reading the datasheet of the phototransistor i noticed that it has a collector-emitor saturation voltage of 200mV, so that means that those 4.5v you use at the beginning of the test and the last value you get (0.15v-0.45v, volts probe), can't be the Vcc but something else.
Could anyone give me some ideas??
Thanks!
At work we assemble some what we call optical sensors (consists of 2 photransistors & 1 LED), after the assembly these sensors are tested to insure that the assembly was well done.
The testing is done with an old test fixture we got many years ago from the manufacturor. (see image)
What we want is to make a new test fixture but using newer components.
We are doing this on our free time, so far this is what we got;
First we looked at what the test fixture really does, and then made a schematic.
What tester does is the following;
First you connect the sensor to the test fixture. The test box has two probes named; volts and milivolts, there you connect a multimeter.
After that is done, you have to turn the voltage adjust knob on the test box, until you read 4.5v on the multimeter connected to the volts probe.
When you have the 4.5v stabilized, you have to read the value of FC1 and FC2 (there's a switch therefore on the box) on the multimeter connected to the milivolts probe.
When these values are according to the specifications (this is done by adjusting a plate on the back of the sensor), you have turn the voltage adjust knob again until you read 0.07V or 70mV on the milivolts probe.
After this is done, you have to read the value on the volts probe, which should be around 0.15v and 0.45v.
After reading those instructions i made a simple schematic, based on what i think is going on, which is;
You use 4.5Vcc (volts probe) on the first step, then you measure the voltage across a resistor connected to each of the photransistors (FC1&FC2, what you read on the milivolts probe).
Then you lower the FC1&FC2 value till you get 0.07V, and then read the Vcc value( volts probe), which should be between 0.15 and 0.45v.
First I tested one sensor on the old test box, and got these values; FC1:3.90v, FC2:3.92v, and the last measurent (when you make the FC values 0.07v) was of 0.16v.
I build the schematic on a breadboard, and was able to get the correct values for FC1&2 (by adjusting a potmeter connected to each of the phototransistors) but when I lower the FC values to 0.07v, I get a reading on the last measurement (volts probe) of about 1.2v, which is way off.
After reading the datasheet of the phototransistor i noticed that it has a collector-emitor saturation voltage of 200mV, so that means that those 4.5v you use at the beginning of the test and the last value you get (0.15v-0.45v, volts probe), can't be the Vcc but something else.
Could anyone give me some ideas??
Thanks!
