Help: Temperature Problems w/ PID'd Silvia

September 23rd, 2009, 9:19 pm

I am having a problem with my temperature regulation on my PID'd Silvia; any ideas would be appreciated.

When I turn on the machine, as it is heating up, the PID reads in the normal range and seems to be operating normally - that is, starting with boiler full on and cycling it off as it approaches the set temperature (about 228F). But when I go to pull the shot, once the pump starts, the PID-displayed temperature instantly jumps to the 260's and I get steam coming out of the grouphead. (The same change in displayed temperature happens if I flick the steam button on and off briefly or if I open the steam wand). Once I flush the machine and fully empty/refill the boiler and it begins returning to set temperature, the machine operates completely normally. This is a new situation in the past few months.

I am guessing that I have a bad thermoprobe in the boiler, as I am pretty sure the temperature is actually up in the 260's even though the PID is reading in the 228's.

Thanks!

{This question also posted on coffeegeek : https://www.coffeegeek.com/forums/espre ... ods/442358}

#2: Post by **cafeIKE** » September 23rd, 2009, 9:29 pm

Assuming the start temperature is close to room temperature and not 40F, the probe is probably OK.

Check the wiring for loose connections.

If you have a VOM, check to see if the output to the SSR is still on after the set point is reached.

Perhaps the SSR is latching? Is there voltage across the heater after the set point is reached.

#3: Post by **JimG** » September 24th, 2009, 12:12 am

You left out the part about it being a relatively inexpensive RTD probe (I saw the post on CG but didn't have any suggestions to offer beyond what you had already surmised).

Slowcountry Tom wrote:But when I go to pull the shot, once the pump starts, the PID-displayed temperature instantly jumps to the 260's and I get steam coming out of the grouphead. (The same change in displayed temperature happens if I flick the steam button on and off briefly or if I open the steam wand).

My guess is that it is the probe, and that the bad behavior is triggered by vibration. A loose wire at the controller would explain the sudden indicated temperature jumps, too. But my money is on there being a bad joint in or around the platinum element inside the probe, or a flaw in the lead wires.

If it is not the probe, then it almost has to be an internal circuitry issue with the PID controller. Sudden jumps in the indicated temperature as you described would not normally be caused by SSR misbehavior.

Jim

#4: Post by **CRCasey** » September 24th, 2009, 1:22 pm

Could this be a false pressure effect from a stuck vacuum breaker?
-c

#5: Post by **JimG** » September 24th, 2009, 2:09 pm

CRCasey wrote:Could this be a false pressure effect from a stuck vacuum breaker?

Don't think so. Lack of a vacuum breaker would affect pressure readings, but not temperature. Besides, there's no vacuum breaker on a Silvia

Jim

#6: Post by **CRCasey** » September 24th, 2009, 4:10 pm

I guess that would tend to eliminate any possible sticking problem then.

#7: Post by **godlyone** » September 25th, 2009, 8:51 pm

could be a bad thermocouple.. but also are you sure your pid is set to the type of thermocouple you are using? [j,k,RTD?]

Also did you make sure that the wires are snugly crimped in the pid? No shorts anywhere?