Superconducting Magnet Systems

The following Video clip illustrates the automated filling of a < 0.25 liter liquid nitrogen dewar of the type normally used for cooling of IR Detectors or CCD devices. Click the video clip icon

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Auto Filling Small Liquid Nitrogen Dewars

Description
This 10 minute, 36 second video is 153,746 KB in size and shows two liquid nitrogen fill cycles. The first half of the video includes a narrated general description of the system and a fill cycle starting with a hot, empty dewar. The second half of the video shows the re-filling of a dewar which already contains liquid nitrogen. The system utilizes the AMI Model 286 Liquid Level Controller operating in Pre-Cool mode. The level sensor used is specialized AMI Flow-Thru design which senses level, vents and acts as a filling tube transferring the liquid into the dewar.

2) A unique Flow-Thru sensor design with integral phase separation for dewars 0.1 to 1 liter in volume.

3) Integral sensors built inside the dewar itself. These are especially useful in applications where maximum hold time between refills is a primary concern.

Autofilling > 1 liter Dewars - The Standard Flow-Thru Sensor allows liquid to pass through the middle of the sensor while simultaneously and continuously measuring the liquid level. This invention is invaluable when autofilling small dewars where only a single port exists. In addition, venting of the internal vessel can also be built into this design and allows for a complete turn-key solution to the problem of filling even the small liquid nitrogen detector dewars with volumes of 1 to 5 liters in size. Photo to right shows flow-thru sensor with integral venting. These can be provided on dewars with a single port of 3/8" or larger.

Autofilling Very Small 0.1 to < 1 liter Dewars - High sensitivity/low noise detectors are often cooled by liquid nitrogen using very compact dewars due to equipment footprint limitations. AMI provides a special flow-thru sensor concept with a built-in phase separation device which is able to fill even the smallest of dewars with only a few inches of liquid height inside the inner vessel. These can be provided on dewars with a single port of 3/8" or larger. Such systems are used in conjunction with the AMI Model 286 Level Controller precool mode which cools the transfer line prior to directing the flow into the small dewar. By doing so the liquid remaining in the dewar at the beginning of a fill cycle experiences almost no loss in level before filling occurs. These systems will autofill and control levels in even the smallest volume dewars accurately and reliably. Typical fill cycles are about 5-10 minutes depending on transfer line lengths used. The Model 286 Level Controller offers a Fill Inhibit feature which allows suppression of a fill cycle start while sensitive data is being collected. Once the relay trigger signal is actuated by the users system logic, the fill cycle and subsequent autofills resume as normal.

Integral Dewar Sensor Autofilling - In certain cases it is advantageous to incorporate the level sensor inside the dewar. Doing so provides only a single coax connection point on the outside of the dewar for connection back to the level instrument. In dewars with very small volumes or all-attitude requirements it is especially useful. Incorporation of the sensor in this manner provides almost no added heat load to the system and maximizes times between refilling while adding the benefits of continuous level measurement. The photograph below shows two such dewars (1.5 liter and 0.25 liter). AMI supplies these detector dewars in a variety of sizes.

Video-Based Small Dewar Autofill Demo