Temperature Control of the Sample
The temperature of the Cryostation is regulated through the platform. The platform thermometer and heater are located right next to each other. The PID actively controls the platform heater to achieve the target temperature on the platform. When the target temperature is set, this is the temperature reached on the platform. Depending on the options installed the sample temperature is typically 0.1-0.5K higher than the platform. If the user has many options installed it may take longer for the sample to reach a temperature close to the platform target temperature. This lag can be anywhere from a few minutes to tens of minutes depending on the thermal conductance of the components between the platform and the sample.
Users may wish to have more control of the temperatures in their system closer to their sample. There are several ways to do this and the best solution may depend on how the user has the system configured.
AGILE TEMPERATURE SAMPLE MOUNT (ATSM)
The ATSM is the most efficient way to increment just the temperature of the sample. This is done with a sample mount, as shown in the image below, which has a built in heater and thermometer. The sample mount is connected to an external temperature controller, the Lakeshore Model 335 or a model with similar capabilities is recommended. This sample mount allows the customer to rapidly scan the temperature from low to high temperatures, to step or ramp temperature, and keep the temperature very stable, all specifically for the sample.
This option is advantageous because the target temperature is set on the Lakeshore temperature controller and therefore changes the temperature of the sample rapidly and locally. The rest of the system will not be subject to the temperature changes of the sample, so if a large temperature range is covered the user will not need to wait for the entire system to cool or warm. Please see the Agile Temperature Sample Mount page for more information. There are two main disadvantages to this option: One is the higher cost; the ATSM will be a more expensive solution than the option outlined below. The other potential disadvantage is the unit requires that you have several pins available, four for the thermometer and two for the heater.
A lower cost alternative to the ATSM is a simple user heater. This option consists of a copper spool wound with resistive wire to achieve a 50 to 200 ohm heater, depending on the range of temperatures needed. The type of wire recommended is manganin, about 10 inches of manganin will yield a 50 ohm heater. It is suggested that the manganin is soldered to phosphor bronze, which serves as the leads to the heater. The manganin can get too warm and burn if it serves as the leads to the heater. To make the heater, cut the needed length of manganin, fold the piece of manganin in half, strip the ends of the wire and solder to 3-4 inches of phosphor bronze. The other ends of the phosphor bronze can be stripped and soldered into the sockets of a connector. The heater only needs to be two pin and should be plugged into the center two pins of the User Heater connector on the sample circuit board.
Once the heater is installed, the power to the user heater can be regulated in the software. This heater is very low profile, so it can be placed close to the sample. Some users even wrap the wire around their sample mount, just be sure that the manganin wires are lagged in place with GE Varnish. A drawback to this style of heater is that only the power to the heater can be set in the software - there is no PID feedback. The User Heater module in the software can be activated conveniently allowing the user to control the heater through the software, but the parameters must be configured properly such that too much current does not go through the heater. Please contact Montana Instruments (firstname.lastname@example.org) on how to properly configure the parameters of a user heater, as this will vary depending on the resistance of the heater.