EMITTER DETECTOR SENSOR

[BHEKI]

Im working on small project which consists of Emitter detector sensor(IR LED transmitter & IR transistor receiver) on the output of this circuit I have a relay(5VDC/28 NT73-2C-s10) which will switch ON as to send 24VDC to my PLC, the problem is the relay doesn't close its contact when I break the beam on my sensor. I suspect that it doesn't receive enough current because when I measured the current going to a relay I got 0.04mA. Is there anyway I can increase this current so as to activate my relay.

 

[Harald Kapp]

Show us a circuit diagram, please. The verbal description is not too helpful.

 

[BHEKI]

Show us a circuit diagram, please. The verbal description is not too helpful.

I tried to post the circuit but I don't know how, I clicked on "IMAGE" option but it asked for URL. Can you direct me on how I can post the circuit

 

[BHEKI]

I tried to post the circuit but I don't know how, I clicked on "IMAGE" option but it asked for URL. Can you direct me on how I can post the circuit

Im sorry think I've managed to upload the circuit.

My sensors are working at 5VDC and I've also used that 5V to supply my relay but when I break the beam the relay doesn't close the contact as to send 24V signal to my PLC. This is da circuit that I had in mind but I would be happy if u can assist me on correcting where you think I might be wrong. Im new to electronic staff. This design project is monitoring the cars that are coming IN and OUT of the car parking.

 

[KrisBlueNZ]

It sounds like the phototransistors are not conducting enough. You said you measured the coil current at 0.04 mA. If your relay is an Electrocomp NT73-2 C S 10 DC5V 0.45 then it has a coil resistance of about 56Ω and will draw 90 mA when fully energised! The phototransistor may not be able to supply that much current even with a mercury vapour lamp shoved right up against it!

What is the distance between the LEDs and the phototransistors? If it's more than a few centimetres, there's no way the phototransistors will conduct heavily enough to activate the relays. You might be able to use very bright LEDs with very narrow viewing angles, accurately aligned, and extra gain (an extra transistor or two) at each receiver. If ambient light is variable, you may get better results using pulsed light - the receiver is able to distinguish the transmitter's light from ambient light (which is not pulsed). Otherwise you might need a different method of detecting cars.

BTW, that circuit (if it worked) would hold the relays closed while the beam is unbroken, and when the beam is broken, the relay would drop out.

Can you describe the project requirements in more detail?

 

[Colin Mitchell]

You only label a relay by the voltage needed to pull it in.

 

[KrisBlueNZ]

You only label a relay by the voltage needed to pull it in.

And the coil resistance (or coil power or coil current, from which the other numbers can be calculated), the contact types and ratings, etc...

 

[(*steve*)]

I think Colin's point may be that the relays are being operated from 5V (and described as 5V) but are labelled as 24V.

 

[KrisBlueNZ]

I think Colin's point may be that the relays are being operated from 5V (and described as 5V) but are labelled as 24V.

Oh, so they are! I don't really know what Colin meant by his comment.

 

[BHEKI]

What is the distance between the LEDs and the phototransistors?

The distance between IR LED and Photo-transistor is about 5cm and I think u are right by saying the Photo-transistor doesn't generate much current as to trigger the relay. Is there any other option of sending 24V signal to my PLC from my 5VDC IR sensor besides using a relay?

 

[BHEKI]

You only label a relay by the voltage needed to pull it in.

Im sorry about the wrong label, my relay is activated by 5VDC not 24V but it will switch 24V to my PLC

 

[BHEKI]

Can you describe the project requirements in more detail?

This project is meant to monitor the cars that are coming inside and outside the car parking. I will be using the IR sensors as to detect the presence of cars, the 1st pair of sensors will open and close the boom gate on the ENTRY side and the 2nd pair open and close the boom on the EXIT side. As the car break the 1st beam on the entry side the output from my sensor send a signal to the PLC and the PLC in response to that will open the boom gate. When the car breaks the 2nd beam the output of the sensor with will send a signal to the PLC as to close the boom. The PLC will also count the number of cars coming inside the parking, also decrement the cars that are coming out. My main problem is the PLC that I have works at 24VDC on its inputs and also give out 24V on the output . My motor driver circuit works at 5V although my output from my PLC is 24V.

I have come out the overall circuit for the whole project but my relays don't seem to be triggered at all.

Will it be okay if I post the circuit?

 

[KrisBlueNZ]

You only label a relay by the voltage needed to pull it in.

Sorry Colin. I misunderstood your comment.

The distance between IR LED and Photo-transistor is about 5cm and I think u are right by saying the Photo-transistor doesn't generate much current as to trigger the relay. Is there any other option of sending 24V signal to my PLC from my 5VDC IR sensor besides using a relay?

Yes. You don't need relays at all. But you will need some way to boost the current from each phototransistor. It might be as simple as a second transistor.



That circuit connects to the 24V field supply from the PLC and provides a signal to a PLC input which is active while the phototransistor is illuminated. VR1 allows the sensitivity to be adjusted down as far as 25 µA collector current, although I think the phototransistor should be able to produce a much higher current than that if the LED is only 5 cm away from it.

This project is meant to monitor the cars that are coming inside and outside the car parking. I will be using the IR sensors as to detect the presence of cars, the 1st pair of sensors will open and close the boom gate on the ENTRY side and the 2nd pair open and close the boom on the EXIT side. As the car break the 1st beam on the entry side the output from my sensor send a signal to the PLC and the PLC in response to that will open the boom gate. When the car breaks the 2nd beam the output of the sensor with will send a signal to the PLC as to close the boom. The PLC will also count the number of cars coming inside the parking, also decrement the cars that are coming out.

OK, thanks for the explanation. So the light beam that falls on the phototransistors will be broken by cars... but you said the LED is 5 cm away from the phototransistor. I don't understand. Are you monitoring extremely thin cars?

My main problem is the PLC that I have works at 24VDC on its inputs and also give out 24V on the output . My motor driver circuit works at 5V although my output from my PLC is 24V.

You might be best to use relays between the PLC outputs and your motor driver circuit then. Or perhaps optocouplers. Can you post the manufacturer names and model numbers for the PLC and the motor controller?

I have come out the overall circuit for the whole project but my relays don't seem to be triggered at all. Will it be okay if I post the circuit?

Yes, please post any information you have. Also can you tell us the I/O characteristics of the PLC.

 

[BHEKI]

OK, thanks for the explanation. So the light beam that falls on the phototransistors will be broken by cars... but you said the LED is 5 cm away from the phototransistor. I don't understand. Are you monitoring extremely thin cars? .

Lol. no Im jst working on a small school project, I will be using car toys for the demonstration.

That circuit connects to the 24V field supply from the PLC and provides a signal to a PLC input which is active while the phototransistor is illuminated. VR1 allows the sensitivity to be adjusted down as far as 25 µA collector current, although I think the phototransistor should be able to produce a much higher current than that if the LED is only 5 cm away from it..

Thanks for the circuit I will try it.

Can you post the manufacturer names and model numbers for the PLC and the motor controller?

The PLC is a SIEMENS SIMATIC S7-200,CPU222
85-264VAC SUPPLY
DI 8*24VDC
DO 6*RELAY,2A

 

[KMoffett]

BHEKI,
Out of curiosity, what was the purpose of resistors R3/R5/R6/R8 in your circuit?

Ken

 

[KrisBlueNZ]

Lol. no Im jst working on a small school project, I will be using car toys for the demonstration.

LOL That makes sense now!

The PLC is a SIEMENS SIMATIC S7-200,CPU222
85-264VAC SUPPLY
DI 8*24VDC
DO 6*RELAY,2A

So the PLC already has isolated relay contacts for its outputs. You can connect them directly to your 5V motor control circuit.

 

[BHEKI]

So the PLC already has isolated relay contacts for its outputs. You can connect them directly to your 5V motor control circuit.

Excuse my ignorance, If my PLC outputs 24V how will that control the 5V motor circuit. Isn't that 24V too much for a circuit that only need 5V. In my case i don't need the motor to run that fast since it only open the boom gate.

 

[KrisBlueNZ]

Excuse my ignorance, If my PLC outputs 24V how will that control the 5V motor circuit. Isn't that 24V too much for a circuit that only need 5V. In my case i don't need the motor to run that fast since it only open the boom gate.

If your output board is "EM222 Relay Output" then the relay outputs are "dry contact". That means they are like a fully isolated switch. You can connect them to any voltage you want; you can even use them to switch AC mains voltage. They are only "24V" outputs if you connect one side of each contact to the 24V supply.

If you have a different type of relay output board, please post the part number and/or link to the documentation for it.

 

[BHEKI]

If your output board is "EM222 Relay Output" then the relay outputs are "dry contact". That means they are like a fully isolated switch. You can connect them to any voltage you want; you can even use them to switch AC mains voltage. They are only "24V" outputs if you connect one side of each contact to the 24V supply.

If you have a different type of relay output board, please post the part number and/or link to the documentation for it.

THANKS for the information again...

 

[BHEKI]

Yes. You don't need relays at all. But you will need some way to boost the current from each phototransistor. It might be as simple as a second transistor.
View attachment 16795

On this circuit how much voltage that must be applied to the IR LED? Is there any other transistor that i cn use in place of the MPSA63