Please help! Converting 0-10v analog signal to 0-1megohm resistance

[toddj]

I urgently need to replace a 1 megohm 20 watt pot with the 1-10v analog output from a plc. The pot is on the dimming circuit of an electronic halogen transformer.

Should I be using a digital pot? Anyone have a circuit for this??

Thanks to all who answer!

 

[rjvh]

Can you post a circuit ??

Robert-Jan

 

[Nigel Goodwin]

I urgently need to replace a 1 megohm 20 watt pot with the 1-10v analog output from a plc. The pot is on the dimming circuit of an electronic halogen transformer.

Should I be using a digital pot? Anyone have a circuit for this??

You have many problems there, not the least the 20W requirement.

I would suggest you need a full circuit diagram of the item to be controlled.

 

[toddj]

I dont have the circuit and the oem is not much help..

Maybe Im doing this the wrong way...

My goal is to use a PLC output to dimm a 71w 12v mr16 halogen bulb using a softstart electronic transformer (120>12v).

The transformer I am looking at has a blue loop of wire that you can cut and insert a 1megohm 20w pot to dimm the electronic transformer.

My other option is to modify the 120v going into the electronic transformer with a pwm type dimmer but I have not been able to find a pwm that will accept a 0-10v or 4-20ma control.

Im going to be building a lot of these..

Any ideas??

Thanks for the input!!

 

[ericgibbs]

I dont have the circuit and the oem is not much help..

Maybe Im doing this the wrong way...

My goal is to use a PLC output to dimm a 71w 12v mr16 halogen bulb using a softstart electronic transformer (120>12v).

The transformer I am looking at has a blue loop of wire that you can cut and insert a 1megohm 20w pot to dimm the electronic transformer.

My other option is to modify the 120v going into the electronic transformer with a pwm type dimmer but I have not been able to find a pwm that will accept a 0-10v or 4-20ma control.

Im going to be building a lot of these..

Any ideas??

Thanks for the input!!

hi,
You could look at this option. ref pdf.

This would give the mains isolation required and would accept PWM inputs.
Use on the transformer primary.

 

[toddj]

Thanks Erick!

What about something like this?

I would just have to drive it with a 16ch cmos

**broken link removed**


or like this?

**broken link removed**

**broken link removed**

.

 

[picbits]

How about taking a step back and using a servo (like the kind found in remote control cars) to operate the Pot ?

Bit crude but easily done.

 

[Willbe]

I urgently need to replace a 1 megohm 20 watt pot with the 1-10v analog output from a plc. The pot is on the dimming circuit of an electronic halogen transformer.

If the 20 W pot carries AC you could use a transformer primary to replace the pot and have the secondary feed a full wave bridge ending in a MOSFET, with the gate being controlled by the analog signal.

 

[toddj]

Ok I had a stupid moment... Its not a 20 watt pot

Its just a 1megohm pot with hardly any current on it. I hooked everything up, cut the blue loop of wire where the pot goes and measured between the hot side of the loop an nutral and I get 64vac, so im guessing that the 1megohm pot reduces the ac voltage from 64vac to 0vac which i think is the feed to a triac??

 

[ericgibbs]

Ok I had a stupid moment... Its not a 20 watt pot

Its just a 1megohm pot with hardly any current on it. I hooked everything up, cut the blue loop of wire where the pot goes and measured between the hot side of the loop an nutral and I get 64vac, so im guessing that the 1megohm pot reduces the ac voltage from 64vac to 0vac which i think is the feed to a triac??

This wouldnt control the firing angle of a triac, it would be either ON or OFF

What about something like this?

I would just have to drive it with a 16ch cmos

**broken link removed**

hi,
The resistive circuit path you are trying to control is carrying 'ac',
the posted logic circuit is a dc controller.!

Can you do that...?

 

[Hero999]

Sorry but using a variable resistor is a silly idea because it's difficult to control using a PLC and lots of waste heat is given off.

Using PWM and an AC or DC solid state relay is probably your best bet.