Stafford Instruments ST535C User manual

ST535C Handbook Page 1
Temperature Programmer Handbook
Issue: 6.002
Date: 10 May 2021
www.staffordinstruments.co.uk
© Copyright 2021 Stafford Instruments Ltd.
TAFFOR
S
D
ST535C

Page ST535C Handbook
2
At a Glance
ZONE 1 ICON
ZONE 2 ICON
ZONE 3 ICON
START/STOP KEY
KILN HEATING
INDICATOR
FIRING INDICATOR
CONTROL KEYS
MIMIC DISPLAY
MAIN
DISPLAY
SEGMENT
DISPLAY
RADIO ICON
PAUSED INDICATOR
MAINS SWITCH
FUSE
ST535C
EVENT INDICATORS
FUNCTION KEY

ST535C Handbook Page 3
Quick Start Guide
Switch on & wait for kiln temperature display
To run a firing program set up previously press
the ► key
To stop the firing at any time press the ► key
again
To review firing data press the ► key to enter the
programming mode
To change firing data press the ▲ & ▼ keys to
change the displayed value
Use the ► key again as necessary to step to the
next firing value or segment to be reviewed or
changed
To mark the end of a program set a ramp rate to
END with the ▼ key
To exit the programming mode either wait 20
seconds or press the ► key to start firing
If the keyboard is locked then press and hold
down the function key for 5 seconds to unlock

Page ST535C Handbook
4
Contents
At a Glance ......................................................2
Quick Start Guide.............................................3
Contents...........................................................4
Features ...........................................................5
Turning On .......................................................6
Programming....................................................7
Temperature Display........................................9
Control Relays..................................................9
Firing ..............................................................12
Cooling ...........................................................13
Operating Notes .............................................14
Adjusting While Firing.....................................15
Error Messages.............................................. 16
Other Features ...............................................18
Sample Glass Programs ................................19
Sample Ceramics Programs ..........................20
WiFi & USB Datalogging Option..................... 21
Installation ......................................................26
Characteristics ...............................................36

ST535C Handbook Page 5
Multi-zone (1,2 or 3 zones)
32 programs each with 32 segments
1 controlled heating / cooling ramp + soak per segment
Soak periods up to 99 hours 59 mins
Ramp rates from 0.1 to 999°/hour + FULL
Ideal for glass or ceramics use
Programs can be altered while firing
Program pause and advance facilities
Keyboard lockable
Delayed start facility - up to 99 hours 59 mins
Power failure recovery
Energy used display
Setpoint display
Alarm buzzer & alarm relay output
2 Programmable control relay outputs
WiFi + USB datalogger option
°C/°F operation
Features

Page ST535C Handbook
6
Turning On
When turned on the ST535C performs a dis-
play test by lighting all of the display segments
and illuminating all of the front panel indicator
lamps.
The version number of the software embedded
within the ST535C is now displayed. If you
need technical support you might be asked for
this code together with the serial number.
Next displayed is the thermocouple type set-
ting. This should match the type of thermocou-
ple fitted to the kiln and can be R, S, K or N
type (R,S,K,N).
The final display will show the kiln temperature.
All other lamps (except the zone indicator lamp
for multi-zone kilns) should be off.
If pressing any key causes LOCKED to appear
then the keyboard has been locked. This is an
anti-tamper feature. Press the function key &
hold down for 5 seconds to unlock.
During firing the star icon will light to show
when heating power is being applied to the
kiln.
This now shows that the keyboard is UN-
LOCKED. To re-lock the keyboard press the
function key & hold down for 5 seconds.
If any mimic panel lamps are on then the ST535C is firing. To stop the firing
press the ► key.
Note: During power up the SEGMENT display shows
the operating units (°C/°F) of the ST535C (Installer
adjustable).
ST535C
F6.00
T/C:R
20oC
LOCKED
UNLOCKED
32oC

ST535C Handbook Page 7
Programming
A firing segment
An ST535C firing segment comprises a ramp followed by a soak period. Two
segments can be used for simple firing (biscuit firing for example) or several seg-
ments can be used per program for complex firing (crystal glazing or glass-
making for example).
The ST535C ramps the kiln temperature at the required ramp rate until the kiln
reaches the soak / target temperature. It then soaks (dwells) at the soak temper-
ature for the soak period. It then runs the next segment until the end of the pro-
gram is reached.
The ST535C is capable of both positive (heating) ramps and negative (cooling)
ramps - as used in glassmaking for annealing. The type of ramp is clearly shown
on the mimic display during firing.
The ramp rate is settable in the range 0.1 to 9.9°/hour then 10 to 999°/hour or
FULL (full power) or END (end of program).
The soak / target temperature is settable over the range 0 to 1550°C (2822°F).
The soak period is settable over the range 00.00 (no soak) to 99 hours 59 mins.
Note: during soaking the ST535C display alternates every 15 seconds
between kiln temperature and soak period remaining.
Cooling Ramp
Heating Ramp
Soak Period
Soak Temperature
(target temperature)

Page ST535C Handbook
8
When not firing there are no indicators lit on
the mimic panel, the run indicator is off and
the display shows the current kiln
temperature.
Altering a program
The controller settings can be reviewed by pressing the ► key.
The first push of the ► key flashes the
program number display. The required firing
program can now be selected with the ▲ & ▼
keys.
Note: holding down the ▲ or ▼ keys causes rapid change of the displayed value.
The next push of the ► key displays the ramp
rate in the range END, 0.1-9.9°/HR, 10-999°/HR
or FULL. This can be altered with the ▲ & ▼
keys. The heating ramp or the cooling ramp
indicator on the mimic panel will flash. END marks the end of the program. FULL
heats or cools as fast as possible.
The next push of the ► key displays the soak
temperature. This can be altered with the ▲
& ▼ keys. The soak temperature indicator
on the mimic panel will flash.
The next push of the ► key displays the soak
period in hours:minutes. This can be altered
in the range 00:00 to 99:59 with the ▲ & ▼
keys. The soak period indicator on the mimic
panel will flash.
The next push of the ► key increments the segment number digit and
firing data for the next segment can be entered.
Program data entry is terminated if END is
selected for a ramp rate with the ▼ key. Pro-
gram data entry is also automatically terminat-
ed if the maximum number of segments have
been entered.
Note 2: to exit programming without cycling through all of the above steps wait 20 seconds without pressing any
keys - the ST535C will revert to the idle display. Alternatively press the ► key to exit programming and to begin
firing immediately.
Note 3: the ◄ key can be used to reverse through the programming steps to correct errors or to exit programming
mode.
Note 1: available ramp rate displays are: END, 0.1 … 999 & FULL. If END is shown but another segment is
required then push the ▲ key to obtain the required ramp rate (in the range 0.1°/hr to 999°/hr). If maximum
heating/cooling is required then push the ▲ key until FULL is displayed. To mark the end of the program push
the▼ key until END is displayed.
20oC
PROG: 1
150oC/HR
600oC
00:15
END

ST535C Handbook Page 9
Temperature Display
To change the displayed zone press either the
▲ or ▼ keys. The zone number icons will
change to show which zone temperature is being
displayed.
This section only applies to multi-zone (2 or 3 zones) kilns. A single zone
kiln will always show the temperature of zone 1 only.
For a single zone kiln the zone icons are not
used and the temperature of zone 1 is always
displayed.
For multi-zone kilns the temperature of each
zone can be displayed. Zone 1 is displayed by
default when the ST325 is powered on.
Control Relay Configuration
While displaying a ramp rate an event output can be
switched on or off by holding in the function key then
pressing either the 1 key or the 2 key. The event
output will be ON when the event icon is on.
The ST535C has 2 control relay outputs.
Control relay 1 can be configured as an event output, a damper control output or a fan
control output.
Control relay 2 can be configured as an event output only.
See the Installation section for details about configuring the control relays.
While displaying a soak period the event output can
be switched on or off by holding in the function key
then pressing either the 1 key. The event output
will be ON when the event icon is on.
Control Relays
Event Outputs
The control relays when configured as event outputs can be programmed to change
state at the start of a ramp and also at the start of a soak period. Thus both ramp and
soak events are possible. The event output is ON (relay contacts are closed) when
the relevant event icon is lit. Prior to running a program both event outputs are OFF
(relay contacts are open). The status of the event outputs is stored within the firing
program.
1020oC
1020oC
1018oC
150oC/HR
00:15

Page ST535C Handbook
10
To enter the damper temperature configuration menu press the ► key and
the key down together while the controller is not running a program (firing
indicator not lit).
Note: in the sequence below if no key presses are detected within 30
seconds the ST535C will exit the menu and damper temperature chang-
es will not be saved.
The damper close temperature prompt is
shown. Release the & keys.
Press the key.
The damper close temperature is now
shown. Adjust with the & keys (hold
down for acceleration).
Press the key.
The damper open temperature prompt is
now shown.
Press the key.
The damper open temperature is now
shown. Adjust with the & keys (hold
down for acceleration)
Press the key.
The instrument will now reset and the new damper control temperatures will
be stored.
Note: in the sequence above it is important that the key is pressed a
total of 4 times else changes will not be saved.
Damper Output
Damper Operation
Prior to firing the damper will be open. During firing, when the kiln reaches
the damper close temperature, the damper will close. The event indicator 1
will be on.
At the end of the firing and when the kiln has cooled naturally to the damper
open temperature, the damper will open. The event indicator 1 will be off.
DAMPER:C
150oC
DAMPER:O
300oC

ST535C Handbook Page 11
To enter the fan temperature configuration menu press the ► key and the
key down together while the controller is not running a program (firing indica-
tor not lit).
Note: in the sequence below if no key presses are detected within 30
seconds the ST535C will exit the menu and fan temperature changes will
not be saved.
The fan start temperature prompt is shown.
Release the & keys.
Press the key.
The fan start temperature is now shown.
Adjust with the & keys (hold down for
acceleration).
Press the key.
The fan stop temperature prompt is now
shown.
Press the key.
The fan stop temperature is now shown.
Adjust with the & keys (hold down for
acceleration)
Press the key.
The instrument will now reset and the new fan control temperatures will be
stored.
Note: in the sequence above it is important that the key is pressed a
total of 4 times else changes will not be saved.
Fan Output
Fan Operation
Prior to firing the fan will be off. During firing the fan will start when the kiln
temperature has risen to the fan start temperature.
The fan will remain on until the kiln temperature has risen to the fan stop
temperature. The fan then turns off and remains off.
The event indicator 1 is turned on while the fan is running.
FAN: ON
200oC
FAN: OFF
700oC

Page ST535C Handbook
12
Firing
To start a firing press the ► key. The firing indicator lamp will flash.
Hint: it is good practice to check that the program is correct by press-
ing the ► key & checking the program number & program contents
before pressing the ► key to start a firing. It is also a good idea to
have a written record of the contents of the firing programs kept and
displayed near the kiln especially if there is more than one user of the
kiln.
With the firing indicator flashing an optional
start delay up to 99 hours: 59 minutes can
be entered with the ▲ & ▼ keys.
Information: The ST535C operates by calculating the amount of energy required by
the kiln every 30 seconds (installer adjustable). If for example 40% of full energy is
required to maintain a particular ramp rate or a particular soak temperature then the
ST535C will apply heating power to the kiln for 12 seconds every 30 seconds. The
kiln heating indicator will light for 12 seconds every 30 seconds. If the kiln has a
contactor then a loud click will be heard both when the kiln heating indicator lights up
and when it goes out. If full heating power is required then the kiln heating indicator
will remain lit. If full cooling is required the kiln heating indicator will remain off.
After 10 seconds, or immediately if the ► key is pressed again, the firing
will commence and the firing indicator lamp will remain lit.
To stop the firing prematurely at any time press the ► key again. The firing
indicator lamp will go out.
Note: during ramping the ST535C will perform either controlled heating or
controlled cooling - as indicated on the mimic display. During soaking the
ST535C display alternates every 15 seconds between kiln temperature and
soak period remaining. At the end of each segment the segment number
display will be incremented.
00:00

ST535C Handbook Page 13
Cooling
Upon completion of firing the ST535C lights all lamps on the mimic display
and the kiln is allowed to cool naturally.
While the kiln temperature is above 40°C the display alternates every 5 sec-
onds between the kiln temperature and HOT.
When the kiln has cooled to less than 40°C the display alternates every 5
seconds between the kiln temperature and END.
To return the ST535C back to idle condition ready for the next firing press
the ► key (or turn off the power to the instrument).
120oC
HOT!
38oC
END

Page ST535C Handbook
14
If the ST535C is programmed to heat the kiln at a faster rate than the kiln is
capable of then the ST535C will turn on full power then wait until the kiln
temperature has risen to the correct temperature before proceeding to the
next ramp or soak segment.
Likewise if the ST535C is programmed to cool the kiln at a faster rate than
the kiln is capable of then the ST535C will apply zero power then wait until
the kiln has cooled to the correct temperature before proceeding to the next
ramp or soak segment.
Kiln too slow
Heating & Cooling Ramps
The ST535C is capable of controlled ramps for both heating and cooling.
The type of ramp required is determined by comparing the required soak
temperature to the soak temperature in the previous segment and is shown
on the mimic display.
► Key Operation
If the ► key is pressed during a firing then the firing will be halted (not
paused). Pressing the ► key again will cause the ST535C to restart the
firing from the beginning. The ST535C will look at the current kiln tempera-
ture and if this is greater than the required soak temperature then the
ST535C will automatically cool from current temperature to the soak temper-
ature. This may not be what is desired so the ► key should only be used
to halt the firing in an emergency.
The program can be paused or program data can be changed while the con-
troller is firing. This is a better option than using the ► key. The program
advance feature is however available to recover quickly from ► key opera-
tion if required (see “Adjusting While Firing” section).
Memory
All programs & necessary data are remembered when the ST535C is turned
off. In the event of power failure during firing the ST535C will automatically
resume firing when power is returned (this feature can be disabled: see in-
stallation section).
Delayed Start
By default the delayed start time period is initialised to 00:00 for each firing.
The ST535C can however be configured to remember the delayed start time
period (see Installation section).
Operating Notes

ST535C Handbook Page 15
Program Pause Facility
WARNING - PROGRAM PAUSE
The program pause facility should be used with care. Program execution is suspended
and the kiln will be held at its current temperature. If left too long at high temperatures
kiln damage could result. Pause will automatically release after an Installer-defined time
period (default: 2 hours - see Installation section).
Adjusting While Firing
Firing values can be adjusted while the ST535C is firing. Also there are pro-
gram pause and program advance features that are particularly useful for
glass work.
Adjusting Firing Values
While firing operate the ► key to select the required parameter as shown by
a flashing lamp on the mimic display. The firing value is shown on the main
display and can now be adjusted with the ▲ & ▼ keys in the usual way. The
contents of the current segment or any segment still to be executed can be
changed. Firing will still carry on as normal while these changes are being
made. The ST535C will return to its normal running display 20 seconds after
key presses cease (or immediately after END is displayed).
Changes made to programs in this way are stored and are used for
subsequent firings.
Program Advance Facility
While firing press and hold down the function key then press the ▲ key to obtain
the (advance) function. The ST535C will sound a short beep and the execut-
ing program will immediately advance one step as indicated by lamps on the
mimic panel. The effect of this is as follows:-
If ramping then the ST535C will switch to soak at the current kiln temperature.
If soaking then the ST535C will advance to the next segment if any, or else it will
end the firing.
Changes made to the operation of the ST535C in this way are temporary and
are not stored.
While firing press and hold down the function key then press the ▼ key to obtain the
װ (pause) function. The ST535C will sound a short beep and the executing program
will pause at the current kiln temperature. The pause indicator (װ) will light. To
release the pause repeat the above action.
While paused, the kiln temperature display will
alternate periodically with a scrolling PAUSED
display and a beep will be sounded.
PAUSED

Page ST535C Handbook
16
Error Messages
Heating error. The kiln temperature is not in-
creasing as required. The kiln has been on full
power for 60 minutes but the temperature has
not increased by at least 2°C.
If the ST535C detects a problem the buzzer will sound and an error message will be
displayed. This error message will alternate with a display of kiln temperature. The
segment number display will show where the error occurred.
Possible causes: kiln door or lid not closed properly or door switch faulty or needs
adjusting. Heater element open circuit or elements too old. Electrical power phase
failure or contactor failure.
Thermocouple or thermocouple wiring open
circuit. Get thermocouple and wiring checked.
Replace thermocouple if necessary.
Thermocouple reversed (kiln temperature appar-
ently less than -40°C). This is an installation
fault. Get wiring checked.
Cooling error. The kiln has been on zero power
for 30 minutes but the kiln temperature has not
fallen by at least 1°C.
Possible causes: contactor failure (contacts welded?) or thermocouple connection
intermittent or high resistance.
Kiln temperature overshoot. The kiln tempera-
ture exceeds the desired temperature by a pre-
set limit.
Maximum firing time exceeded. The length of
the firing has exceeded an installer selectable
limit.
Maximum room temperature exceeded. The
internal temperature of the ST535C has exceed-
ed an installer selectable limit.
Possible causes: kiln room vent fan failure, kiln room too small, ventilation grills
blocked, damper or bung left open, controller mounted too close to kiln.
To obtain more information on the error press the ◄ key. The first press will display
the maximum temperature reached in the firing. The second press will display the
length of time that the error has been present. The buzzer will mute.
ERROR:1
ERROR:2
ERROR:3
ERROR:4
ERROR:5
ERROR:6
ERROR:7

ST535C Handbook Page 17
All these error messages cause the ST535C to terminate the firing. The alarm buzzer
will sound once per second. To reset the ST535C turn off the power to the instrument
and have the fault investigated and rectified by your installer or kiln service engineer.
Technical note: these error messages will cause the alarm relay
to open.
Note: these error messages are provided to detect kiln faults
and so offer some protection to the kiln.
Program Error. This error message is displayed if
a potential error is detected within the firing pro-
gram when the ► key is pressed to start a firing.
The alarm buzzer will sound 3 times and the seg-
ment display will show the suspect segment number. To clear this error press the ►
key. The ST535C will now enter programming mode to allow the suspect program to be
viewed and altered if necessary. If a fault is found then correct it. If no fault is found
then press the ► key again to force the firing program to start. A potential program-
ming error is defined as a very low ramp rate to a very low temperature. Such a pro-
gramming fault might cause very long firing times with potential kiln damage.
Firing Program Errors
Internal data conversion circuit (ADC) error.
Maximum allowable differential temperature
between zones exceeded. The temperature of
zone 2 or zone 3 has varied from zone 1 by an
installer selectable limit.
ERROR:8
ERROR:9
ERROR:P

Page ST535C Handbook
18
Other Features
Energy Used & Setpoint Displays
Press and hold down the function key then
press the ◄ key at any time to show the
amount of electrical energy used in kWh.
During a firing the energy used so far is
shown. After a firing the total energy used for the firing is shown. This infor-
mation is stored while power is off and is only reset to zero when a new firing
is started. If the value displayed is always 0.0 then the kiln power rating has
not been configured - see Installation section.
Operating the ◄ key a second time shows the current set-point (the temper-
ature which the ST535C is currently trying to achieve).
Keyboard Lock Facility
The keys on the ST535C can be locked so that pressing them has no effect.
This is an anti-tamper feature used to ensure that the operation of the
ST535C or the program data cannot be altered by un-authorised people.
The ST535C can be locked when it is idle (not firing) or while it is firing. It
cannot be locked while it is being programmed.
Power Failure Recovery
If power fails during firing then the ST535C recovers as follows:-
For power failure during start delay the ST535C times off the remaining start
delay when power returns. For power failure during ramping the ST535C
continues the ramp it was previously executing. For power failure during
soaking the ST535C ramps back up to soak temperature at the correct ramp
rate then applies the remaining soak period. This recovery scheme can be
disabled if required (see Installation section) - the ST535C will then lock up
with FAIL displayed and kiln off in the event of power failure.
Press and hold the function key down for 5
seconds to lock or to unlock.
12.5KWH
LOCKED
UNLOCKED

ST535C Handbook Page 19
Sample Glass Programs
Program No.
Program
Description
Seg 1
Ramp
Rate
°C/hr
Seg 1
Soak
Temp
°C
Seg 1
Soak
Time
hr:mn
Seg 2
Ramp
Rate
°C/hr
Seg 2
Soak
Temp
°C
Seg 2
Soak
Time
hr:mn
Seg 3
Ramp
Rate
°C/hr
Seg 3
Soak
Temp
°C
Seg 3
Soak
Time
hr:mn
Seg 4
Ramp
Rate
°C/hr
Seg 4
Soak
Temp
°C
Seg 4
Soak
Time
hr:mn
Seg 5
Ramp
Rate
°C/hr
14-6mm Float Glass Fuse 150 538 00:10 FULL 840 00:20 FULL 538 00:45 182 427 00:15 END 24-6mm Float Glass Slump 538 538 00:00 FULL 824 00:20 FULL 538 00:15 182 427 00:00 END 36mm Bullseye™ Fuse 222 677 00:30 333 795 00:10 FULL 482 01:00 83 371 00:01 END 46mm Bullseye™ Slump 167 640 00:10 FULL 482 01:00 56 371 00:01 END - - - 56mm Spectrum System 96™ Fuse 200 500 00:00 FULL 804 00:12 FULL 540 00:40 150 510 00:20 END 66mm Spectrum System 96™ Slump 155 704 00:20 FULL 540 01:30 FULL 510 00:10 26 371 00:00 END 7Bottle Firing Cycle 170 510 00:00 250 780 00:10 FULL 510 01:00 70 400 00:30 END 8Low Stain 200 570 00:10 FULL 516 00:30 100 300 00:00 END - - - 9High Stain 200 665 00:10 FULL 550 00:20 FULL 516 00:30 100 300 00:00 END
The ST535C is provided pre-programmed with the glass firing programs below. These programs may be modified as required.

Page ST535C Handbook
20
Sample Ceramics Programs
Program
Number
Program Name Seg 1
Ramp
Rate
°C/hr
Seg 1
Soak
Temp
°C
Seg 2
Ramp
Rate
°C/hr
Seg 2
Soak
Temp
°C
Seg 2
Soak
Time
hr:mn
Seg 1
Soak
Time
hr:mn
Seg 3
Ramp
Rate
°C/hr
11 Slow Bisque 60 600 FULL 1000 00:0000:00 END
12 Normal Bisque 100600 FULL 1000 00:0000:00 END
13 High Bisque 100600 FULL 1140 00:0000:00 END
14 Brush-on
Earthenware Glaze
1000°C (Cone 6)
100 300 FULL 1000 00:0000:00 END
15 Standard Earthenware
Glaze 1100°C
100 300 FULL 1100 00:0000:00 END
16 Earthenware High
Temperature Glaze
1140°C
100 300 FULL 1140 00:0000:00 END
17 Mid-Range
Stoneware Glaze
1200°C
100 300 FULL 1200 00:0000:00 END
18 Standard
Stoneware Glaze
1260°C (see note)
100 300 FULL 1235 00:0000:00 END
19 Onglaze 780°C 100400 FULL 780 00:0000:00 END
20 Lustre 750°C 100400 FULL 750 00:0000:00 END
Note
It has been found that a kiln controller will give greater heat work as the temperature
increases. Therefore to achieve a stoneware firing of cone 8-9 we suggest setting the
final soak temperature to 1235°C. A slight adjustment can then be made after the first
firing. It should be remembered that kiln controllers are indicators of temperature and
the effects of faster or slower firings may cause extreme variations in the end result.
This is known within ceramics as “heatwork”. Cones are measures of heatwork and it
is strongly recommended that cones are always used in conjunction with a kiln
controller to appreciate the differences between heatwork and temperature indicated
by the controller. Stoneware firings will also demonstrate the greatest potential
differences between heatwork and indicated temperature.
The ST535C is provided pre-programmed with the ceramics firing programs
below. These programs may be modified or over-written as required.