Wavelength Electronics WTC3293, Datasheet And Operating Manual

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WTC3243 TEMPERATURE CONTROLLER
ADDITIONAL TECHNICAL NOTES
This section includes useful technical information on these
topics:
• Connecting an External Potentiometer
• DAQ Protection -- Change Defaults
• Eliminating Trimpots
• Changing the P GAIN to a Fixed Value
• Increasing Proportional Gain Range
• Changing the I TERM to a Fixed Value
• Changing LIM to a Fixed Value
• Changing Onboard Setpoint Trimpot to a Fixed
Resistance
• Safe Operating Area & Heatsink Requirements
CONNECTING AN EXTERNAL POTENTIOMETER
RSET:
Set the VSET SOURCE jumper in the “X” position
(subject to DAQ Failsafe Protection circuit). Place the
potentiometer’s CW terminal in the pin marked 2.5 V.
Connect the potentiometer’s wiper (W) to the pin marked
RSET and CCW terminal to the pin marked COM. Do not
use less than 2 kΩ resistance, or the 2.5 V will droop.
HSET:
Remove the VSET SOURCE jumper (not subject to
DAQ Failsafe Protection circuit). Place the potentiometer’s
CW terminal in the pin marked 2.5 V. Connect the
potentiometer’s wiper (W) to the pin marked HSET and
CCW terminal to the pin marked COM. Do not use less
than 2 kΩ resistance, or the 2.5 V will droop.
(-)
(+) FAN
REN
HSET
COM
W
CW
CCW
2.5 V
TB2
SET T
ACT T
LIMA
LIMB
COM
RSET
TB3
Figure 28. Example Wiring—External RSET Adjustment
DAQ PROTECTION -- CHANGE DEFAULTS
If the voltage set by the external input drops below 0.3 V,
the failsafe circuit is triggered and the setpoint defaults to
1 V. This prevents overheating of the load if the input signal
fails. The 1 V default is designed for 10 kΩ thermistors
(1 V = 25°C). This default is only used with RSET.
Figure 29. DAC Protection Circuit Settings
To override the failsafe default, remove D1, use the HSET
input, or the onboard trimpot. To change the failsafe trip
point, change the voltage divider between D1 & D2.
Use Equation 13 to calculate the appropriate value.
Equation 13. Calculate Failsafe Trip Point Voltage
V
TRIP
= 6.6 D2
D1 + D2
Where:
D1 default is 100 kΩ.
D2 default is 4.99 kΩ.
D1 should not go below 100 kΩ.
To change the default once tripped, change the voltage
divider between D3 & D4. Use Equation 14 to calculate
the appropriate value.
Equation 14. Calculate Failsafe Default Voltage
V
DEFAULT
= 6.6 D4
D3 + D4
Where:
D3 default is 49.9 kΩ.
D4 default is 9.76 kΩ.
D3 should not go below 49.9 kΩ.
D1, D2, D3, and D4 are 0805 size resistors.