Heater Block

The curvetrace program allows controlling the temperature of the DUT during curve tracing. To this end, the DUT is clamped onto a large metal block equipped with heater elements and a temperature sensor. The heater block temperature is controlled by a PID controller in the curvetrace software, which reads the temperature sensor and adjusts the power of the heater element as needed. This is illustrated in the following diagram:

Heater block diagram

See Construction of a heater block for DUT temperature control for an example of the design and construction of a curvetrace heater block.

  • To allow tight control of the DUT temperature by the heater block, its thermal inertia should be much larger than that of the DUT. A large block of copper is recommended, which exhibits a large specific heat capacity and thermal conductance.

  • Power resistors are used as heater elements. The resistor array is powered by a programmable PSU which is controlled by the curvetrace program (see Supported power supplies for supported PSUs). The heating power from the resistors and PSU should be adapted to the heat capacity of the heater block.

  • A Maxim DS18B20 digital temperature sensor is used to read the heater block temperature. The 1-Wire bus of the DS18B20 is connected to the computer using a USB-TTL adapter cable (for example FTDI TTL-232R-RPI) as follows:

    • DS18B20 data pin ⟷ TXD and RXD joined together on the USB adapter cable

    • DS18B20 GND and supply pins joined together ⟷ GND pin on the USB adapter cable

The configuration of the heaterblock for the curvetrace program is specified in the curvetrace_config.txt file by adding a [HEATERBLOCK] section as follows::

[HEATERBLOCK]

PSU_COMPORT       = ...
PSU_TYPE          = ...
TEMPSENS_COMPORT  = ...
TEMPSENS_TYPE     = ...
TBUFFER_INTERVAL  = ...
TBUFFER_NUM       = ...
HEATER_RESISTANCE = ...
MAX_POWER         = ...
KP                = ...
KI                = ...
KD                = ...

  • PSU_COMPORT and PSU_TYPE: COM port and type of the PSU used for the heaters (see also Power supply configuration and Supported power supplies for details).

  • TEMPSENS_COMPORT: COM port of the temperature sensor

  • TEMPSENS_TYPE: type of temperature sensor. Currently, only TEMPSENS_TYPE = DS1820 is supported.

  • TBUFFER_INTERVAL: time between temperature readings (in seconds)

  • TBUFFER_NUM: number of temperature readings that must be consistent with the target temperature in order to assume stable temperature conditions

  • HEATER_RESISTANCE: resistance of the combined heater resistors (in Ohm)

  • MAX_POWER: maximum heating power

  • KP, KI, KD: coefficients of the PID controller