Operating instructions
If you are using a portable, separate controller, you will
need to install the thermocouple onto the kiln. See the sep
-
arate TnF 2 installation instructions.
Preventing an Overfire
Even though a digital controller turns off the kiln auto
-
matically, you should monitor the kiln during firing. This is
to prevent a possible overfire.
Remain nearby while the kiln is firing.
Check the kiln occasionally.
Set the temperature alarm (page 12) to
remind yourself to check the kiln. If you
are too far away to hear the alarm, you
might try using a baby monitor.
After the kiln fires to completion, dis
-
connect the power. It is okay to turn off
the power to the controller while the
kiln cools to room temperature.
Theory of Operation
The temperature you are firing to is called
the target temperature. After the Sentry reaches the target
temperature, it can also hold that temperature.
The Sentry fires at a controlled heating rate. The rate is
figured in degrees per hour. If you selected a rate of 100°
per hour, it would take 10 hours for the furnace to reach
1000°. Rate is similar to miles per hour.
In summary, the Sentry does three basic tasks:
1) It fires at a controlled heating rate, or speed, mea-
sured in degrees of temperature change per hour.
2) It fires to a target temperature.
3) It can hold the target temperature.
The Sentry fires in segments, or stages. A segment is a
controlled heating rate to a target temperature. A segment
can also have a hold. Shown in the chart in the left column
is a segment with a target temperature of 1250°, a rate of
625°, and a hold of one hour.
The two parts of a segment:
I
: The temperature changes.
I
: The temperature remains the same.
Heating rate is figured in degrees per hour. The recom
-
mended heating rate for the material you are firing is usu
-
ally available from your supplier. It also varies
depending on the thickness of the material.
A segment can have only one ramp and
only one hold. Therefore, if you need more
than one hold, you will have to add additional
segments to the firing. Firing to a temperature
at a single rate would need only one segment.
Reasons to add more segments:
I
To change the heating rate.
I
To add a hold somewhere below the
shut-off temperature.
I
To control the cooling rate.
The diagram below shows a 3-segment firing. Two seg
-
ments were used on the way up in temperature. Another
segment was added for controlled cooling.
To figure how many hours a segment will take to fire,
subtract the current temperature from the target tempera-
ture and divide the result by the heating rate. In the dia-
gram in the left column, the firing time is 1250° - 80° (room
temperature) = 1170 ÷ 625 = 1.87 hours.
After the Sentry has finished firing the last segment, it
will turn off power to the heating elements.
6 Ramp-Hold
This segment will reach the target temperature of 1250° in 2 hours, then
hold that temperature for 1 hour.
Here is a simple 3-segment program. Segments1 and 2 each have
a hold. Segment 3 is a controlled cooling segment.
“Rate” is how
many degrees per
hour the kiln will
climb in temper
-
ature. (Or how
fast it cools
during a con
-
trolled cooling.)