Application Tips
Thermoelectric cooler (TEC) is a semiconductor device which is characterized by unique heat pump performance with high efficiency, compactness and durability. The unique ability of TECs to heat and cool, permits them to lower temperature of an object below ambient as well as to stabilize temperature of objects in widely varying ambient conditions.
Here we mention some application tips that can help in optimal use of TECs.
Mounting
Power Supply
Environment
Handling
Heat Dissipation
Reference Data
Brief Summary
PID CONTROLLER


Close loop DC control is the best solution for TEC operation. It provides most effective use of TECs.
In practice two control methods are in use:
 ProportionalIntegral (PI) Control
 ProportionalIntegralDerivative (PID) Control
For most applications PI Control looks is enough. But RMT recommends to use most complex PID control loops.
Usually there is not so much difference in hardware of such two types (PI and PID), only one additional coefficient  a derivative circuit to the PI controller which improves the transient response of such control.
Effectiveness of PID/PI controls depends on correct adjustments of parameters of the Loop:
 Kp, the proportional constant, controls the loop gain.
 Ki, the integral constant, offsets errors.
 Kd, the derivative constant, affects the damping rate.
Calculation of the parameters requires knowing or to examining some specific properties of TEC. One of the methods  ZieglerNichols tuning approach.
Name  Description  Comments 

Process gain  dT/dU (or dT/dI)  Response of the TEC to applied power 
Time constant  τ  Time constant of controlled system 
Dead time  τD  Delay of the TEC system response 
By these parameters it is easy to calculate parameters of both PI or PID controls:
Control Method  Kp  Ki  Kd 

PI  0.9 K  3.3 τD  — 
PID  1.2 K  2 τD  0.5 τD 
where K = time constant / (process gain × deadtime) .
In many cases tuning of the PID parameters is done by trials and errors. It is quite long way and requires experience. There are highend TEC Controllers which provide autotuning functions. Even with PID loop parameters obtained this way, final fine tuning is very useful.
Knowledge of object of the control (TEC) is very important for such working. Rough estimations on the basis of the knowledge make PID tuning easier and more effective:

Process gain
Roughly estimated value of process gain correlates with maximal performance parameters of a TEC. There are TEc maximal parameters DTmax and Imax or Umax. Thus
Dead time
To estimate value of deadtime it is possible to apply assumptions of most mathematical methods which are used to close loop:

Time constant
 RMT provides TEC time constant τTEC in standard specifications.
 Time constant τTEC of a TEC mounted to header or heat sink is doubled (~2 x τTEC).
 If an object is mounted onto cold side of TEC, the time constant becomes considerably higher. It depends on thermal capacity of cooling object:
where C  thermal capacity of the object; ΔT  desired temperature difference; Q  cooling power of TEC.