Numerical Methods

Vötsch VT4002 climate chamber

The Vötsch VT4002 climate chamber can simulate environments within a temperature range from -40 °C up to 135 °C. The model at the Institute of Solid State Physics has no humidity control. The climate chamber is equipped with a PID controller that has one temperature sensor attached and regulates the heating and cooling of the chamber. The PID controller also offers the possibility to run predefined temperature test profiles. Because temperature changes are very slow (in the seconds range) there is no real benefit in using those test patterns directly from the PID as compared to controlling the climate chamber from a PC (because timing is not critical).

When working with the chamber there are basically three things one can do:

1. Set a new target temperature (setpoint value).
2. Read the current temperature of the temperature sensor.
3. Enable or disable the heater / cooler.

Manual operation

There is a touch screen on the frontpanel that can be used to operate the climate chamber. There is also a web interface (http://129.27.158.42/simpac) that can be used to set the target temperature and monitor the sensor temperature.

Refer to the Vötsch VT4002 User's Manual for details.

Using Python

The most convenient way to control the climate chamber is using Python. When a new temperature setpoint is given, it takes a while for the temperature to stabilize and often the temperature oscillates around the desired temperature. To ensure that the temperature has stabilized, a Python function was defined to wait until the temperature stabilizes to within a specified accuracy for a certain time. This function is,

 
go_to_temperature(temperature, target_accuracy, settling_time)

The program execution is delayed until the temperature stays between (temperature - target_accuracy) °C and (temperature + target_accuracy) °C for at least (settling_time) seconds. Only then will the program execution continue.

An example script that uses this function is,

More details of the VT4002 Python library

The Python library (voetsch.py) uses the requests-package (see here for installation instructions) to interface with the web-server of the climate chamber and provide accessibility to the basic functions. Make sure that you have installed the requests-package prior to establishing communication (otherwise you will get an error).

To communicate with the climate chamber you need to have the IP address, the username and the password (you will find these information on the front of the climate chamber). The python code that opens communication to Vötsch VT4002 is,

from voetsch import VT4002 # define connection parameters ip_address = "129.27.158.42" username = "myuser" password = "mypass" # connect to the climate chamber climate_chamber = VT4200(ip_address, username, password)

Once communication has been established, you can use the following commands to control the climate chamber.

Read out the current temperature measured by the climate chambers temperature sensor and print the result to the console, you can use:

temp = climate_chamber.get_actual_temperature() print('Current temperature (°C): ' + str(temp))

You can also read out the currently set target temperature by using the following command:

target_temp = climate_chamber.get_target_temperature() print('Target temperature (°C): ' + str(target_temp))

If you want to know the status of the climate chamber (ON or OFF), you can get that information with this command:

status = climate_chamber.get_chamber_status() print('The chamber status is: ' + str(status))

To enable or disable the climate chamber you can use commands climate_chamber.enable() and climate_chamber.disable().

Now let's assume you want to heat up the chamber to 42.5 °C. After connecting to the climate chamber you therefore need to set the setpoint temperature and enable the climate chamber. The code for such an operation would look like this:

climate_chamber.set_target_temperature(42.5) climate_chamber.enable()

The climate chamber will instantly begin with the heat-up. The Python process will instantly continue (so it will not wait until the target temperature is reached). If you want your program to wait until a specific temperature is reached, you need to ensure that yourself. This can be done by querying the current temperature repeatedly in a while loop until the target temperature is reached.

Keep in mind that (specially on thermal system that are PID controlled) you might have oscillations around the target temperature and it takes some time until the temperature is stable again. It is good practice to check not only the temperature but to check if the temperature stays stable within defined boundaries for a specified time. To make programming easier, there is a function in the voetsch-library that does exactly that for you. The command climate_chamber.go_to_temperature will block further Python program execution until the target temperature is reached and stable. Let's have a look at the following code:

climate_chamber.enable() climate_chamber.go_to_temperature(50, target_accuracy=0.2, settling_time=60) print('This line will be printed when the temperature is stable.')

SimPati PC Software

Vötsch offers proprietary software that is shipped with the climate chamber. It communicates with the climate chamber through an unknown protocol and can be used to control and configure the climate chamber. The software consists of a server module that handles communication to the climate chamber and a frontend user software. For most applications the use of the SimPati software is too complicated. If you have special demands or want to change the PID behavior, refer to the documentation:

SimPati Anleitung (deutsch)
Simpati Simserv Anleitung (de)
SimPati Manual (english)
Simpati Manual (english)

• Vötsch VT4002 User's Manual
• voetsch Python library