Eric, good idea on the dash pot. 2 questions though, 1) should the dash pot be a multi turn precision? and 2) since my range is at the "other end" of the pot up top, shouldnt this dash pot be up there instead? Not toward the ground side. I am between 0 ohms and 100 ohms off R2 for my range. I am having a hard time seeing how I can get to near "0" ohms in this manor.
Stu
Stu
hi stu,
The dash post could be a single turn general purpose pot.
If the cable run to the dashpot is long it would be an idea to use a length of screened cable.
If you are Vsensing about 4.5V and a 6V2 ref diode is being used, I cannot see why the multiturn setpot is at one end.?
If you need to have the setpot higher, putting the dashpot in the top will make it worse.
For example:
say the Vsetpot is 5K and there is a
5K dashpot in the bottom.
The junction of the two pots will Vset be at 3.1V [half Vref], if you now trim the set pot so the wiper is halfway then the Vset will be at 4.65V, which is in the switching voltage region you require.
As you are adding the dashpot, like I said it would be advisable you add that 10K fixed resistor from the Vsetpot wiper to the LM393 input.
Its important to note, that the higher the resistive value of the dashpot the more coarse will be the 'user' adjustment
even though its greater range.
By experimentation you should be able to determine the optimum resistive values of the Vsetpot and the dashpot.
As a check measure the voltage at the top of the Vsetpot, it should be 6V2.