TEC manual

Intoduction

The TEC controller can be attached to a variety of peltier elements. It features a linear H bridge output capable of driving several amps in either way through the peltier element. The TEC can be supplied with 5.5 to 12V. It requires 2 NTC’s (10k @25Deg), one on either side of the peltier element. mounting example 1, mounting example 2. The NTCs are included in the delivery.

Features

the electronics is protected against overtemperature
the regulated (active) side of the peltier is protected against undertemperature as well as against overtemperature
the unregulated (passive) side of the peltier is protected against undertemperature as well as against overtemperature
protection against weak powersupplies
settable maximum current
settable control loop parameters
preset temperature from software
communicates with either RS232 or RS485, jumper selectable
opto transistor output signals loss of closed loop operating mode
LED signals closed loop operating mode or being in range
Comprehensive Windows GUI
Can be powered by switch mode powersupplies
Manufactured according to the european RoHS regulations
Fullfills the relavant CE norms EN 60950-1, EN 61010-1, EN 61000-6-2, EN 61000-6-4

Specifications

Accuracy

down to 0.005Deg, depending on the temperature. The resolution of the 16bit ADC corresponds to 0.002Deg at 25Deg. Peltier elements must not be powered with pulsed current. Therefore the output of the TEC module is a linear H bridge. It can be powered with 5.5 to 12V, depending on the required voltage. For power dissipation reasons, the supplied should be kept as low as possible. The maximum current is not yet specified, it is limited by the heat dissipation of the heatsink switches itself off. The output is able to deliver at least 8 Amps for a short time.

Connectors

10 pin flat ribbon cable header for communication
8 pin Weidmüller SL3.5/8/90 for sense, power and peltier element, the other connector is provided

Size

approx 100mm wide x 63mm deep x 20mm high incl. Flat ribbon cable connector connected. Mounting holes are to be drilled.

Operation

The temperature on either side of the peltier is measured with a 16Bit ADC giving values between 0 and 65535. The temperature is not linearized as this would imply a polynomial of at least 6th order plus floating point calculations. The temperature can be preset by software or by an optional onboard potentiometer. The difference between actual temperature and preset temperature (setpoint) is called error signal, we refer to it as delta. A PID controller with adjustable parameters calculates the output current. The nonlinear FET output is linearized upon power up. When the maximum current before the supply voltage drops below a fixed limit, an error is signalled. Make sure the maximum current is set accordingly. Upon an error condition, the TEC goes open loop and the current is set to zero. This state is latched, meaning it has to be reset by software or power off-on.

First steps

Connect the power and the signals as :

The orange analog connector is cabled as follows, with pin 1 being to the top, beside the aluminum :

pin	meaning
1	positve peltier terminal
2	positive powersupply 5.2 to 12V
3	negative peltier terminal
4	GND of powersupply
5	precision 2.5V and common of NTC
6	active NTC, on the regulated side
7	passive NTC, on the unregulated side
8	switched GND do not connect

The +2.5V on pin 5 in respect to GND pin 8, is supplied from the electronics.
The power for the peltier is connected at pin 2 in respect to pin 4.
The peltier is connected between 1 & 3
The active side NTC is connected between 5 & 6
The passive side NTC is connected between 5 and 7

The communication connector is cabled as :

pin	as RS485	as RS232
1	+5V out, can be omitted	+5V out, can be omitted
2	GND, reference for RS485	GND, reference for RS232
3	data+, bidirectional or tx only	nc
4	data-, bidirectional or tx only	nc
5	data+, rx only	nc
6	data-, rx only	nc
7	nc	Tx
8	nc	Rx
9	interlock, current in	interlock, current in
10	interlock, current out	interlock, current out

Next steps

Start the Windows GUI.
The GUI tries to get a reply to a few standard commands by itself and will fill the returned values into the GUI
Click into the ‘Echo’ panel. Some numbers indicates the device communicates.
got the next page and tick the "auto update" checkbox top left.

Enter a value into the editbox at Setpoint (register), eg 26.32 and press the arrow button
Enter a value into the editbox at Max Current, eg 1.22 and press the arrow button
Enter a value into the editbox at Max Act NTC, eg 60.0 and press the arrow button
Enter a value into the editbox at Min Act NTC, eg 10.0 and press the arrow button
Enter a value into the editbox at Max Pas NTC, eg 40.0 and press the arrow button
Enter a value into the editbox at Max Pas NTC, eg 15.0 and press the arrow button

A speciality of these inputs is that either floating point values or integer values are accepted. Floating point values must have a decimal dot
now go to the next page and check the "auto update" checkbox top left
If the Error code in the settings panel is "00", then everything is working as expected.
Changing the maximum current requires recalibration : click ‘ramp cool’ and ‘ramp heat’,
both might take a few seconds each. After recalibration, the TEC knows DACthrLeft, DACmaxLeft.
These values determine the behaviour, the max current it not used anymore afterwards.
Except that it is required at a new powerup.
Check the polarity of the peltier module : enter a value of 3000 into the editbox beside scurrent
The value of activeNTC in the ‘measurements’ panel should rise. If it falls, swap the wires to the peltier module.
A click to "Current = 0" in the ‘settings’ panel switches the current off.
Back on the configuration page, click ‘mode, control loop = closed’.
The ErrorCode on the in the settings of the third page should now turn to "04 : wait timer", meaning the TEC starts controlling the temperature. The graph on the dynamic page (the third) shows the delta signal, the temperature difference. After a certain time the delta approaches zero and stays there plus minus a few bit.
There might be a difference between setpoint-activeNTC and delta. This comes from a delay
in the sampling and its transmission.
A double click clears the graph. Changing the speed changes the update rate of the screen, but has no other effect.

Errors

The TEC signals Error 0x80 (missing peltier) : The max current may be set too high, when
the max current is not reachable, the peltier is assumed missing.
The TEC stops with 0x02 ‘Undervoltage’. The powersupply drops the voltage and the
‘Supply’ reaches ‘MinSupply’ at ‘Maxcurrent’. Decrease the Maxcurrent.

RS422 communication

The RS422 communication mode is full duplex operation.
For some introduction have a look at the ibrt short message protocol

RS232 communication

The RS232 communication is straight forward. For some introduction have a look at the ibrt short message protocol. See the ‘TEC communication manual’ for further information

Interlock

The interlock is shorted while the TEC operates in closed loop. The green LED is lit at the
same time. The closed loop mode is left either by a software command (mode) or due to an error.
The green LED will switch off then and the interlock opens. For bus operation the interlock has
to be cabled in a special way :

Bus operation

Except for the interlock signal, a flat cable can be used to connect up to 32 devices. The
interlock, by definition is a series connection of devices, whereas a flat cable would connect
them parallel. Therefore use the following cableing at each node except the last one :

Note that several TEC connected to a weak powersupply with long thin cables could lead to
erratic behaviour when all of them draw maximum current. At power up, the power supply test is delayed linear to the ID, such that they don't draw maximum power at the same time.

Undervoltage protection

The H-bridge is capable of drawing substantial currents from a powersupply. A weak powersupply,
and/or long thin cables cause a voltage drop at the TEC module. The used CPU, though a
low voltage type, would scramble the EEPROM at lower voltages. Therefore the cpu itself samples the supply and switched itself off when such a condition is detected.
When the cpu detects undervoltage, the TEC is switched of and the state is latched, meaning it
has to be reset by software or by switching the power of and on.

Though this chapter sounds complicated and the feature could be regarded as bug, it allow to
adapt to various setups while performing close to the limit. The safe side is : have a strong
powersupply connected with short thick cables. Set MaxCurrent sufficiently low.
Or use a separate supply for the power part.

MaxCurrent

the current is measure as voltage across a 0.01 Ohm shunt, then multiplied with 40. The value is
samples with a 10bit ADC. This value is then compared the Maxcurrent setting. This is only
done at powerup or upon the rampcurrent commands, when the DACs for the FETs are calibrated.

Note that setting the current by software in the openloop mode allows a current above the
Maxcurrent to be set. If the powersupply is strong enough, and the heat dissipated by the
electronic is carried away, that’s fine. Otherwise the undervoltage error may be triggered
if the MaxLED is set correctly, or the electronic overtemp error may be triggered.

Temperature protection and measurement

the following temperatures are monitored :

sensor	compared for under temperature	compared for overtemperature
NTC on passive side of peltier element	MinPassiveNTC	MaxPassiveNTC
NTC on active side of peltier element	MinActiveNTC	MaxActiveNTC
NTC on the electronic	none	MaxIntNTC

The NTC’s are connected to the +2.5V reference and have resistor (Rbase)to GND. The middle voltage
is sampled with a 10bit ADC referenced at the reference of +2.5V, and is therefore independent
of the supply. The temperatures are calculated as follows :

RNTC(T):=RNTC(Tref)*exp(beta*((1/(T+273))-(1/(Tref+273))))
where
T is in degrees Celsius
Tref is 25 Degrees Celsius
RNTC(Tref) is 10k Ohm, unless noted otherwise
beta is 3530, unless noted otherwise

The ADC reading is then

ADC:= Rbase/(RNTC+ Rbase)*1024

where Rbase is 10k Ohm, unless noted otherwise

The ADC values are compared with the settings. Note that MaxIntNTC is quasi fixed to 795 being
about 60 degrees Celsius. It may be changed during operation but will be reset to the default
value at power up. The temperatures are compared in the open loop and in the closed loop mode.
Exceeding them causes the TEC to switch off and signal an error.

The GUI allows you to enter the temperatures as floating point values.
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last update: 10.sept.06

Copyright (99,2006) Ing.Büro R.Tschaggelar