Sensor Repair¶
The cryolab has a number of temperature sensors that measure temperatures on the cold heads. Some of the sensors are installed on the cold head cylinder and are used by the system the are installed on. Other sensors are connected to bands or are mounted directly to the cold head cylinder for testing. Below are some of the sensors that commonly fail and the techniques for repairing them.
DT-670-SD-QL32-0.7¶
The DT670 diode is an off the shelf diode that is reasonably accurate between 30-100ºK with a tolerance of ± 0.25ºK. More information can be found on Lakeshore.com
Troubleshooting¶
Warning
Diode packages are extremely fragile and can break if mishandled. Please refer to the un-mounting instructions for the safe removal of the copper tape and sensor.
The sensors will produce a false reading on Labview when the leads are broken or if the insulation has worn through and the signal is shorted. The sensor must read room temperature if not mounted to the cold head cylinder. If it is mounted it should be reading the temperature of the cylinder.
Note
Cold head cylinders that have recently been removed from the heaters will read in the low 300ºK range. Room temperature is approximately 295ºK.
When troubleshooting the sensor that is mounted to a band there are a few locations where the sensor can become damaged. Use the configuration below and follow the troubleshooting steps. Inspect the band for any signs of strikes or damage to the sensor and wire under the copper tape. If damage is discovered on the tape you will have to remove the tape to reveal the wire and diode package.
- Secure the band to the cold head cylinder.
- Mount the cold head in the swivel table.
- Connect the Labview temperature sensor cables
- Connect a helium line to either supply or return on the cold head (this ensures proper grounding).
- Orientate the cold head cylinder upward.
In Labview, make sure that the test sector is active and reading. You must watch the temperature for any changes during your troubleshooting.
- Press lightly with your finger around the copper tape for any open connections.
- Take note of any changes in temperature during this process and the location it occurred.
If there is an open connection or short to ground discovered under the tape, follow the instruction of un-mounting the sensor from the band before proceeding.
Disconnecting Back Shell¶
If no noticeable change in temperature is produced with light pressing on the sensor package and wire then there might be a break in the wire in the wire at the DB9 solder connection.
Remove the DB9 connector back shell.
Inspect the solder points for broken wire.
Un-Mounting DT670 Sensors¶
Un-Mounting From Bands¶
The DT670 sensor can be mounted to bands for easy and safe on-off of cold head cylinders. The copper tap that holds them on can fold the sensor package in half when removing the tape which will cause the leads to break off of the package.
To remove the tape begin from the wire lead end and slowly peel back the tape using a finger to hold down the exposed leads.
Using a wooden pick, gently hold down the lead tips as you continue to slowly pull back the tape.
Continue this technique for the sensor package
Un-Mounting from Cylinders¶
In some cases it is necessary to mount the loose sensor package to the cylinder using copper tape. The same techniques for un-mounting from the band apply to un-mounting from the cylinder.
To remove the tape begin from the wire lead end and slowly peel back the tape using a finger to hold down the exposed leads.
Using a wooden pick, gently hold down the lead tips as you continue to slowly pull back the tape.
Continue this technique for the sensor package