Fire alarm using a PTC as a sensor.

[m_b_anf]

I have been trying to do a circuit with the following charcteristics:

The output is a siren connected to a 230 V 50 Hz network. The control circuit will use a 9 V battery as power supply and an operational amplifier must be used, the siren will be activated with a relay. The alarm will be activated when the temperature is higher than 60 degrees celsius. (The simulation was made with simulide)

I also used a BJT transistor to control the passing of the current, I think the control circuit and input circuit is correct, somehow the relay doesn't close and so the led doesn't switch on. What is wrong with my circuit?



Moderators note : expanded schematic.

 

[Alec_t]

Check the switch in the relay. Do you see a problem there?
What do you think the comparator output will be if the PTC resistance increases?

 

[bertus]

Hello,

Check your schematic.
What is the type number for the comparator?
Does the comparator need a pull-up resistor?
How is the relais powered?
Can the bridge work, the way you have drawn it?

Bertus

 

[AnalogKid]

There is no common ground. The input circuit, comparator, and output circuit all must be referenced in some way to the same DC potential. They do not necessarily have to be hard wired together - there are some instances where you might want a DC offset between the input and output.

But in your case, they must be hard-wired together.

If you add a unique reference designator to each component, the exact connections can be described. Without reference designators, you're on your own.

ak

 

[danadak]

Also output of comparator should have a series R to the transistor to limit
base current. Current should be limited to ~ Relay coil current / 10. Yiou
should also have a snubber or diode clamp to manage L based transients
from damaging the transistor.



R2 should be ~ 10 x R1, R1, depending on relay coil current needed, 100 - 1000
ohms. Ibase = Ic / 10 to help you compute it.


Regards, Dana.

 

[davenn]

What is wrong with my circuit?

lots

Dana has given you the correct info regarding the transistor and relay wiring.
The way you have wired it, the relay will never operate as it isnt getting any power.
Also, even with that fixed, the LED will not light as it doesnt have a complete power supply

In reality, if the only thing you are operating is the LED, then the relay isnt needed and the LED and
its series 1k resistor can be put in place instead of the relay and it's snubber diode

EDIT, one moment you are talking about a siren ""output is a siren connected to a 230 V 50 Hz ""
Then you talk about a LED
So which are you really using ?
If a 240V siren, then a relay will be needed and it's switching contacts need to be capable of
240VAC and whatever current the siren unit requires ??


cheers
Dave

 

[bidrohini]

Here is a PTC-based fire alarm circuit that you can follow:

By the way, you can also consider using a temperature sensor+arduino instead:

What are Temperature Sensors - The Engineering Projects

In today’s tutorial, we will discuss What are Temperature Sensors. The most significant parameter in industries and different engineering project is a te

www.theengineeringprojects.com

 

[bidrohini]

You can consider AD8615, OPA128, or LT1793.

 

[Delta Prime]

The output is a siren connected to a 230 V 50 Hz network. The control circuit will use a 9 V battery as power supply and an operational amplifier must be used, the siren will be activated with a relay. The alarm will be activated when the temperature is higher than 60 degrees celsius

"An operational amplifier must be used."That sounds very much like a class assignment.Is this school work?
If not. High temperature sensing is a very good indicator of a fire... Unless of course you have a heater set at 60° c.

 

[dave9]

High temperature sensing is terrible indicator of a fire, unless it's just the wax slug in a sprinkler head, activating it to save property.

Smoke preceeding the temp rise will suffocate inhabitants, and the smoke is (usually) detectable using existing tech, far in advance of the temperature rise.

 

[Delta Prime]

High temperature sensing is terrible indicator of a fire, unless it's just the wax slug in a sprinkler head, activating it to save property.

Smoke preceeding the temp rise will suffocate inhabitants, and the smoke is (usually) detectable using existing tech, far in advance of the temperature rise.

Poppycock I got flames shooting out of my head.
Heat alarms (detectors) respond to high temperatures of 135°F (57°C), not smoke or fire, and are ideal . They are another useful part of any fire safety plan.
Smoke alarms are not designed for use, in most areas & depends on application. Many heat alarm models can be connected to a home's or commercial Business fire detection system so that if the heat alarm sounds, the smoke alarms will as well.
But as stated before unless you have a heater set at 57 ,60° c.
We're talking on a breadboard for learning purposes educational.

 

[dave9]

There's nothing ideal about being knocked unconscious from lack of oxygen from the smoke, long before it got hot enough to set off a heat detector. Having the extra time to evacuate can be crucial.

I'm sure there are some special circumstances where the opposite is true but try it for yourself, light a fire in an enclosed area and see which happens first, smoke detector goes off or temp exceeds (whatever, you have to have some margin).

Typically a smoke detector will go off before there is even ANY measurable change in temperature significant enough to design for. There would be a smaller change in temp than common situations like having the heater turn on in winter or A/C turn off in summer.

 

[Delta Prime]

The alarm will be activated when the temperature is higher than 60 degrees celsius. (The simulation was made with simulide

@dave9 Here is a PTC-based fire alarm circuit that you can follow:

 

[kellys_eye]

I'm with @dave9 on this. Smoke detection AND flame detection.

Having worked in a marine environment (not a good place to be when there's fire around) you need all the warnings you can get and smoke detection is a primary device.

If this is a simple case of developing an op-amp comparator circuit then float your boat (another marine reference) but if it's for a real world application then stick to well developed, commercial stuff.

 

[Delta Prime]

I'm with @dave9 on this. Smoke detection AND flame detection

Well I never!
Very well go with Dave I want you both to stay the heck out of my garage.
I smoke alarms as well... in the kitchen. How you think I know when dinner's ready?

Heat Alarms

Safety tips to help your fire department increase community awareness about where to use heat alarms.

www.usfa.fema.gov

 

[bidrohini]

Check the output of the OPAMP. Maybe it is not changing to switch ON the BJT. However, I find temperature sensors preferable. These are quite easy to use with microcontrollers.

What is Thermistor - The Engineering Projects

In today’s tutorial, we will discuss What is Thermistor. A thermistor is a semiconductor temperature sensing module, their value of the resistance is

www.theengineeringprojects.com