HARDWARE CONCEPTS
Output 3
Output 3 is an internal fail-safe relay that allows setting of temperature limits which if
exceeded, will result in the output to the TEC(s) to be shut down (turned off). Using
Alarm 3 high and Alarm 3 low ([A3hi] and [A3lo]) provides the means to shut
down power to the TEC(s) should user set limits be exceeded, thus protecting the
TEC(s) from potential damage.
TURNING OFF OUTPUT 3 WILL TURN OFF THE CONTROLLER OUTPUT.
TO REMOVE ANY TEMPERATURE ALARMS SIMPLY SET THE TEMPERA-
TURE ALARMS OUTSIDE THE OPERATING RANGE OF THE TEC(S).
PLEASE SEE APPENDIX J FOR MORE INFORMATION ON OUTPUT 3
Current Limits
Under normal control situations, the current limit of the output is accomplished by
setting the “Current Limit Above” and “Current Limit Below” variables within the Main
Menu ([Il`a] and [Il`b]). The “Above” and “Below” offer added flexibility
when used in conjunction with the “Current Limit Set point” ([Ilsp]). The “Current
Limit Set point” is a temperature around which you would want to limit the current
either “Above” or “Below”. A very basic example would be to protect from thermal run
away during a cooling application with a marginal heat sink. In this hypothetical situa-
tion you could set the [Ilsp] variable to 30°C (just over ambient) and set the
[Il`a] variable to 0.0 percent and the [Il`b] variable to the maximum current
while cooling. We’ll say 50%. So during normal operation (process temperature
“Below” the [Ilsp] or 30°C) the controller would allow up to 50% current (the
setting of [Il~b]). However, if the fan on the heat sink of the TEC should fail and
the heat generated caused the controlled temperature to rise above the
[Ilsp] of
30°C, the controller would limit the current to the
[Il`a] setting (or 0.0 percent).
Note: These current limit variables are in percentage of the maximum current of the
controller. For instance, a 10 ampere rated controller with [Il`a] and [Il`b]
set to 10%, will essentially limit the current to 1 ampere. Notice that setting the two
current limits (
[Il`a] and [Il`b]) to the same thing essentially sets a single
current limit no matter what the process temperature or the Current Limit Set point is!
ALPHA OMEGA INSTRUMENTS CORP. Instruction Manual
Series 800/850 Thermoelectric Cooler Controller Page 19
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