Hello
In the place I work we purchased 2-10v actuators but have 0-10v controller.
The easiest would be to change the actuators bot I was wondering if someone here has an idea...
What I need is a circuit that will amplify a 2v input to 3v but wont amplify any input greater than 3v. doesnt have to be precise.
I have 24vac to work with.


For those who are interested it is an actuator of a water valve on an air conditioning system. What is happening now is that when the controller outputs 1V for example (when temerature is around setpoint) instead of letting through a bit of water it doesnt do anything at all.
I can set the controller to put out 5 steps of 2 volts but in the lowest step it still wont do anything. That is why I was thinking maybe it can be solved.
And that is why I dont need it to amplfy above 4V

thanks for reading

 

Would it work to add a small fixed offset to the signal, like 0.5V?

 

hi,
What is the current rating of the actuator/controller.?

E

 

attn:crutschow
0.5 offset might not give the desired result. it might be to small of a signal at 2.5V.
Also I dont know the consequences of feeding it with 10.5v at maximum working voltage.
I think ideally 3.5V would have the system in "cruise mode"

attn:ericgibbs
I am not sure (i can check the datasheets) but just to be clear it draws operational current from the 24vac the 0-10 is just reference voltage.. sorry if I misunderstood and I can check if it makes a differnce

thanks

 

Not having seen the d/sheet for the actuator does it it have its own internal drive amplifier and the controller sends a 0 to 10Vdc low current control signal.?

E

 

yes exactly. simply a control signal

 

A 12V linear regulator (7812 type) with a shutdown input would work. The shutdown input would be driven by a comparator to keep the regulator off when voltage is less than 2 V. Above 2V the output follows the input.

 

hey papabravo
I dont quite understand what you are suggesting.
what do i gain with the 7812 ? and how does it bump up the voltage ?

 

Would it work to add a small fixed offset to the signal, like 0.5V?

That's what I'm thinking. Add 2v offset.

I'd bet the valve isn't linear on the top end. Hitting wide open a little early won't matter.

12 volts isn't going to hurt. If worried it could be clipped at 10v.

 

Below is the simulation of a circuit that uses a window comparator to add an offset to the signal between about 2V to 3.5V. Is that what you want?

Note that I didn't show how to generate the +12Vdc. You could add a rectifier, filter, and voltage regulator to generate the +12Vdc from the 24VAC.

 

how would i clip it to make sure it doesnt pass 10V?

 

attn: crutschow
nice one. what aould i need to add to turn my 24 vac to 12vdc that this circuit runs on?
some capacitor and the 7812 i assume? remind you that 24vac is what i need to work with because i would put this circuit near the actuators (in their connection box)

 

hey papabravo
I dont quite understand what you are suggesting.
what do i gain with the 7812 ? and how does it bump up the voltage ?

It doesn't bump up the voltage it outputs 2-10 volts for a 0-10V input.
It is well know that a linear regulator output will follow the input when the input is less than the regulated output voltage. A 7812 will output 0-10V for a 0-10V input. A 7812 with a shutdown input can be used to output 0V when the input is between 0V and 2V.

 

attn: crutschow
nice one. what aould i need to add to turn my 24 vac to 12vdc that this circuit runs on?
some capacitor and the 7812 i assume? remind you that 24vac is what i need to work with because i would put this circuit near the actuators (in their connection box)

The circuit takes less than 5mA so a linear regulator will dissipate very little power. You could use a 1N4848 diode (or similar) connected to the 24VAC, a 100μF capacitor to ground, and a 10V zener diode to feed the input of the 7812. You need to put the zener in inverse series (back-to-back) with the diode to drop the voltage safely below the 35V maximum input rating of the 7812.

 

'0-10V to 2-10V'
'What I need is a circuit that will amplify a 2v input to 3v but wont amplify any input greater than 3v.'
'And that is why I dont need it to amplfy above 4V'

I'm confused as to exactly what voltage range you actually need?

 

attn: papabravo
What output will I get at 2v ?

attn: crutschow

"quote:You need to put the zener in inverse series (back-to-back) with the diode to drop the voltage safely below the 35V maximum input rating of the 7812."

wouldn't the ac voltage become 34vdc ? I multiplied by sqrt2.

 

I'm confused as to exactly what voltage range you actually need?

I might of confuse things a bit . but to make it simple I need that a 2v output from controller will give 3V to actuator because the actuator still doesnt react at 2v being a 2-10v

 

......................
attn: crutschow

"quote:You need to put the zener in inverse series (back-to-back) with the diode to drop the voltage safely below the 35V maximum input rating of the 7812."

wouldn't the ac voltage become 34vdc ? I multiplied by sqrt2.

True, which is too close to the 7812's maximum rating of 35V for good reliability. That's why I added the series zener, to drop it to about 23V.

 

Assuming your actuator control input is high impedance (>10k), here's one way you could get a 3-10V (approx) output without the use of an opamp, albeit there's a constant 3V output when the controller is in the 0-3V range:

 

attn:alec_t
I really like that your design does the job very simply!
And yes this is what I need in order to not replace the actuators.
What would need to be changed if I needed to tweek the output a bit? Can I use a potentiometer in the circuit ?
I just have to check the impendance because I really am not so sure about that, hoping though.