help with sensor replacement

[cbiblis]

I was hoping that someone could tell me what i could get that would replace this sensor that i could purchase at digikey . Velleman nv - Item - Details
I can't find anything that matches the specs and i don't know what i can bend on and what i can't. This is used on a thermostat. Thanks for the help.

 

[crutschow]

We'd have to know more about the application and the accuracy requirements to know for sure what specs can be bent. But if the application isn't too critical a typical 10kΩ NTC thermistor, of which there are many at Digikey such as this Digi-Key - BC2301-ND (Manufacturer - NTCLE100E3103JB0), should work.

 

[mneary]

What you can bend in the specs depends on the circuit and its function. The resistance is important for almost any circuit. In a thermostat, you just need to make sure it won't self-heat too much (but a 10k ohm thermistor won't self-heat much at normal voltages, e.g. 3V is less than a milliwatt). If it's a fixed setting somewhat near 25C, then the B-value isn't very important. However if it's in a circuit that's already calibrated then B-value is important.

 

[cbiblis]

Here is the schematic for the thermostat also any suggestions on the relay chatter would be great, it only happens on 30 percent of the circuits i build. As for the accuracy, i shoot for .5 degrees and a hysteresis of 1 degree. This happens on most of these circuits however i can deal with a 1 degree variance and a 1 degree hysteresis. the transformer is 120v to 12v 100ma. Thanks again.

 

[Boncuk]

Hi cbiblis,

the power supply you designed is the absolute minimum to create DC. With single way rectification and and a smoothing cap of 470µF the ripple voltage is ~1Vpp at 60mA total current flow. (40mA for the relay and 20mA for the LED, not taking into account the current flow of the evaluating circuit). The relay activation voltage is about 2V below nominal.

First, connect a 47µF electrolytic cap parallel with the relay coil and see if it increases stability.

If that won't help much, connect another rectifier diode into the ground path at the secondary transformer tap. This will decrease voltage output slightly, but ripple frequency will double - probably causing the relay not to chatter.

Boncuk


P.S. Eagle has a tool called "split". Avoid slanted net lines by splitting the wires to straight lines, and also avoid putting nets through an IC - about that: (attachment)

 

[cbiblis]

Hi cbiblis,

the power supply you designed is the absolute minimum to create DC. With single way rectification and and a smoothing cap of 470µF the ripple voltage is ~1Vpp at 60mA total current flow. (40mA for the relay and 20mA for the LED, not taking into account the current flow of the evaluating circuit). The relay activation voltage is about 2V below nominal.

First, connect a 47µF electrolytic cap parallel with the relay coil and see if it increases stability.

If that won't help much, connect another rectifier diode into the ground path at the secondary transformer tap. This will decrease voltage output slightly, but ripple frequency will double - probably causing the relay not to chatter.

Boncuk


P.S. Eagle has a tool called "split". Avoid slanted net lines by splitting the wires to straight lines, and also avoid putting nets through an IC - about that: (attachment)

Thanks for the reply Boncuk. I did every thing that you suggested and they are still chattering. I also tried replacing the led with a diode 1N4148 to save power still not working. Do you have any more suggestions?

 

[cbiblis]

I really need to find a schematic or have one designed. I'm so aggravated with this one. It was designed for a green house and i modified it to work on a chicken incubator. I guess what i really need is a whole new design. One with a PWM to really tighten up my temp variances. I need a reliable foundation for the controller that i plan to build for my incubators.
All in all, i would like to fix the thermostats that i have right know then i will need a schematic that uses some off the same parts, cause i have enough components to build 20 more. Or i can fix this design finish building the 20 i have parts for then trade in the design to a better one. Help with this would be great to.

 

[Boncuk]

Thanks for the reply Boncuk. I did every thing that you suggested and they are still chattering. I also tried replacing the led with a diode 1N4148 to save power still not working. Do you have any more suggestions?

Hi cbiblis,

there is the possibility that the hysterisis is too small. This causes the output of the OpAmp to slowly rise or decrease output voltage, thus switching the transistor on and off rapidly around the trip point.

Another cause may be the power supply. If the relay pulls in supply voltage as well as reference voltage are affected by the voltage drop leading to unstable conditions. (considering a transformer with 100mA output current)

I'll redraw the circuit (and a PCB design) using a dual OpAmp TLC272P (which I suppose is more accurate than the LM324) and an 78L12 voltage regulator to supply the OpAmp and the reference voltage source. The relay and LED will be connected to the unregulated voltage. If the voltage is too high a low value resistor will drop it to make it safe for the relay coil and LED.

It would be helpful to know the nominal relay coil resistance/current.

Regards

Boncuk

 

[cbiblis]

**broken link removed**

 

[Boncuk]

**broken link removed**

Do you want to fry relays or use them for switching purposes?

A 5V relay won't last long being supplied with unregulated 12V!

That page also contains an offer of 12V (10A/125V) even cheaper (US$5.99 instead of the 5V type for US10.99).

Also it pays to use good brand relays for reliable function over a long time period. I use only FINDER relays.

BTW, I have redesigned your circuit for a greater span of presettable switching temperature, including a 12V stabilized power supply and a stabilized voltage reference.

The PCB layout is single sided with one wire jump to force circuit ground to go off the smoothing cap connected to the regulator output pin.

Board dimension is: 3.35X3.025".

Regards

Boncuk

 

[cbiblis]

Do you want to fry relays or use them for switching purposes?

A 5V relay won't last long being supplied with unregulated 12V!

That page also contains an offer of 12V (10A/125V) even cheaper (US$5.99 instead of the 5V type for US10.99).

Also it pays to use good brand relays for reliable function over a long time period. I use only FINDER relays.

BTW, I have redesigned your circuit for a greater span of presettable switching temperature, including a 12V stabilized power supply and a stabilized voltage reference.

The PCB layout is single sided with one wire jump to force circuit ground to go off the smoothing cap connected to the regulator output pin.

Board dimension is: 3.35X3.025".

Regards

Boncuk

Sorry the 12v relays that you saw on his listing are the ones that i have. When i went back to find the specs for you i clicked on the wrong listing sorry. Thanks for the design i will give it a try. Also do you have a schematic to go with it? I ask only because I'll have to build my own brd file from eagle. I try to size my boards in rectangles to fix my project boxes. By the way what will be the temp range? and what will be the hysterisis? Thanks again

 

[Boncuk]

Hi ciblis,

of course I will provide schematic and PCB layout as Eagle files. Please PM me your email address. I'll be glad to change the design for you if you provide the part values and PCB dimensions including drill positions for mounting holes.

I changed the reference input voltage divider for voltages between 762mV and 4.573V. You might change values according to your intentions. The feedback resistor of 220K is unchanged.

I have problems finding out the NTC resistance value at a given temperature.

Attached is the Vishay NTC datasheet from which you probably can read better than I do. (Too many numeric values. )

Regards

Boncuk

 

[cbiblis]

Hi ciblis,

of course I will provide schematic and PCB layout as Eagle files. Please PM me your email address. I'll be glad to change the design for you if you provide the part values and PCB dimensions including drill positions for mounting holes.

I changed the reference input voltage divider for voltages between 762mV and 4.573V. You might change values according to your intentions. The feedback resistor of 220K is unchanged.

I have problems finding out the NTC resistance value at a given temperature.

Attached is the Vishay NTC datasheet from which you probably can read better than I do. (Too many numeric values. )

Regards

Boncuk

Just to let you know i PM ed you my email addi yesterday.