Chattering relay

Looking for ideas to eliminate chattering of my relays that are activated depending on the ADvalue that is read from the analog input.

The Analog value is filtered through DT_Analog module (Analog oversampling to 12 bits).

But on the decision point, relays are chattering on/off as the analog value is slow changing.

Code:

---

gosub getADC
    'ADvalue=abs (ADvalue-818)
    if ADvalue < upper then
        relay.0=1
    else
        relay.0=0
    endif
     
    if ADvalue < mid_upper then
        relay.1=1
    else
        relay.1=0
    endif
   
    if ADvalue < mid then
        relay.2=1
    else
        relay.2=0
    endif
   
    if ADvalue < mid_lower then
        relay.3=1
    else
        relay.3=0
    endif
   
    if ADvalue < lower then
        relay.4=1
    else
        relay.4=0
    endif

---

Any ideas?

Ioannis

the obvious way is note when a relay state change occurs
then inhibit any further state change until a determined period has elapsed

Hysteresis, maybe?

Thanks.

I tried hysteresis but there are 4 decision points and things are getting messy.

I set up Timer 1, counting seconds. The main loop runs fast but the relays are set (or reset) only after the defined time delay, now 10 sec.

Seems OK.

Ioannis

Quote:

---

Originally Posted by Ioannis

Looking for ideas to eliminate chattering of my relays that are activated depending on the ADvalue that is read from the analog input.

The Analog value is filtered through DT_Analog module (Analog oversampling to 12 bits).

But on the decision point, relays are chattering on/off as the analog value is slow changing.

Code:

---

gosub getADC
    'ADvalue=abs (ADvalue-818)
    if ADvalue < upper then
        relay.0=1
    else
        relay.0=0
    endif
     
    if ADvalue < mid_upper then
        relay.1=1
    else
        relay.1=0
    endif
   
    if ADvalue < mid then
        relay.2=1
    else
        relay.2=0
    endif
   
    if ADvalue < mid_lower then
        relay.3=1
    else
        relay.3=0
    endif
   
    if ADvalue < lower then
        relay.4=1
    else
        relay.4=0
    endif

---

Any ideas?

Ioannis

---

how about something like this for virtual hysteresis:

Code:

---

    if ADvalue < upper then
        if upperbufferflag=0 then 'add the buffer only once
            upper=upper+upperbuffer:upperbufferflag=1
        endif
        relay.0=1
    else
        if upperbufferflag=1 then 'subtract the buffer
            upper=upper-upperbuffer:upperbufferflag=0
        endif
        relay.0=0
    endif

(typical for each instance)

---

picster

Thanks picster.

What I finally did is this:

Code:

---

if ADvalue < upper-hyst then
            relay.0=1
        elseif ADvalue > upper+hyst then
            relay.0=0
        endif

---

The user through menu, can set the hyst (hysteresis) window.

Also the update of the relays is not done immediately but every xx seconds also user defined.

Both these did the trick.

Ioannis

VERY slick solution. Great for reference for cases where hysteresis is needed, thanks for sharing!

Picster

Thanks picster. It works very reliable, especially in my case where the value does not change too quickly.

Ioannis

I see your software worked but you might need more capacitor filtering of the A/D voltage input, especially when operating relay

I always do Averaging or Darrels Analog Oversampling from 12 to 14 bits. 16 bits is better of course but takes too long.

Ioannis

The other option (just spitballing here) would be to put a cap across the coil. It slows down the coil release. Not very useful if you need the relay to release fast, but I have used it in a couple of oddball cases over the years.

Andy