Re: Problems with Rancilio Silvia and Fuji PXR3 PID

On 25 Oct 2008 14:31:29 GMT, ton <birdie@hotmail.com> wrote:

>I haven't been here for a while and I hope that there are still PID experts here
that can help me with a problem I have since a few days.
>About 3 years ago already, I installed a Fuji PXR3 to my Rancilio Silvia and
followed the instructions on "Murph's Silvia PID Page". Since then everything
worked perfect. I have the PID set to 110*C, with FUZY
>on,and the temperature stayed very stable within + and - 0,1 or 0,2*C. The last few
days (I hadn't changed anything meanwhile) however, every now and then and very
randomly, the temperature rises in between to
>around 150*C. After that it falls slowly to 110*C again. I have tried the autotuning
already a few times again, but that doesn't solve it permanently.
>Is there anything I can do to have the Fuji working correctly again or do I have to
assume that it is defective due to it's life span ?
>Thanks in advance.
>ton
>

You'll have to watch the heater light and the temps closely and "catch
it in the act."  As soon as the heater light turns on continuously
with the machine idling at setpoint, and/or the temperature starts to
rise above setpoint, then quickly check the voltage across the low
voltage DC terminals on the SSR (normally terminals 3 and 4).

Here are the possibilities:

1.  Voltage at the DC terminals is low (below 1V), but the heater
light and heater are on. If true, then
a.   SSR is bad, or
b.   (less likely) you have an  intermittently shorting steam switch
on the Silvia, or
c.  your heater is failing and intermittently shorting to the boiler
shell (test by plugging Silvia into GFCI outlet).

2.  Voltage on the DC terminals is high (above ~5V).  If this is true,
then the PXR3 is probably faulty.  Output should be low/off when the
temperature is above setpoint and rising.  Check to see if the LED
output indicator on the face of the PID is off when the output is
(erroneously) high.

3.  Voltage on the DC terminals is between 1V and 4V.  If true, then
PXR3 is probably bad, or you have a loose wire.  This is no man's land
and the SSR doesn't know how to respond.

A bad thermocouple, or a bad thermocouple connection, could cause a
false temperature indication.  I lean away from this in your case,
though, since the 150C reading corresponds with the high limit of the
steam thermostat, and the 110C reading corresponds with the setpoint
of the PID.  I'd expect more random readings from a loose or bad t/c.
Nonethelss, still worth tightening the connections and visually
inspecting for corrosion (assuming you followed Murph's directions and
used a type J).

My money would be on the SSR being the problem.

Jim
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