Custom sensors are available from AMI to meet your individual application requirements. Below is a partial list of the custom capacitance sensors that AMI provides. As an additional service AMI can provide materials certifications, vacuum leak rate certifications, or pressure test certifications.

Bent Sensors - Useful in systems with molded dewar collars or requirements for radial exiting connections. These continuous reading level sensors offer much improved performance over previously available point sensor based units. Such requirements are often very useful in germanium gamma ray detector (HPGe) liquid nitrogen autofill systems and Silicon (Li) x-ray detector liquid nitrogen autofill systems. See photos. AMI can provide such systems as part of a new installation or, in many cases, retrofit existing equipment with a completely new continuous reading autofill system.


LOX Sensors - Made using virgin Teflon and stainless steels, these sensors contain no epoxies or other materials that could act as a fuel source in liquid oxygen systems. Special care is taken to minimize residual oils during the construction process, however, special cleaning is required for liquid oxygen service. Although LOx cleaning services are not provided by AMI, once arrangements are made by the customer with the cleaning specialists of their choice, AMI can drop-ship directly to them.


Point Sensors - Point sensors can be provided using the same proven capacitance technology used in our continuous sensors. Such sensors can be used as redundant backup reading to a continuous sensor in highly critical applications or in a smaller package (as gas/liquid indication in closed pipe systems) such as heat exchangers or phase separators.


High Pressure Sensors - Level measurement systems for cryogenic non-FM-Approved applications up to 4,000 psig are available. When required, the pressure boundaries are modeled and analyzed for stress using state of the art finite element programs. Hydrostatic pressure tests and certificates are readily available. When required, ASME certified pressure vessel welders and specialized welding techniques are employed.


Open LN2 Bath Sensors - Some applications use open baths of liquid nitrogen (food freezing, cryogenic metals treatment, shrink fitting of parts, etc.). Effectively controlling the level in such baths is complicated by the presence of moisture in the surrounding air. This moisture will easily condense on the exposed portion of the level sensor, ultimately forming an ice buildup that can render the level measurement ineffective. AMI has developed a sensor construction which eliminates this problem and will provide reliable readings in open baths for an unlimited time period. For food service applications, AMI offers Sanitary flanges, polished surfaces and crevice-free fillet welds - sensor construction materials are limited to stainless steels and Teflon.


Frost-Proof and Water-Proof Sensors - Capacitance sensor signals can be effectively "shorted" by the presence of electrically conductive water getting in the connection between the capacitance plates. This is most commonly a problem in the coaxial connection at the upper end of the rigid sensor. AMI offers several solutions to this problem and fully understands the requirements to alleviate such problems. Frost-proof sensors keep the electrical connection out of the ice formation. Our Water-Proof kit seals this junction and prevents moisture from reaching the connection. This is especially useful in food service or pharmaceutical environments requiring routine wash down cleaning. When the active portion of the cryogenic probe itself is exposed to moisture the probe can either be dried or given an initial cooling prior to reintroduction of the level measurement into the control loop. The later is an effective method because ice is non-conductive and no longer effects the measurement after the moisture is frozen.


Segmented Sensors - When tank heights exceed 15 feet it is worthwhile considering a segmented sensor. These sensors come in sections and are either bolted together with a miniature flange or screwed together. Sensor sections are factory assembled and disassembled to ensure proper fit. Each sensor section is match marked for proper identification and assembly instructions are normally provided. Upon request all fasteners can be predrilled for lock wire to ensure no parts come loose even under high vibration conditions.


High Flow Rate Sensors - Certain level applications require a very fast electronic signal update rate combined with specially designed sensors to provide a suitable level signal under extremely rapid level change conditions. Many of AMI's level instruments update the analog output reading every 50 mS and are therefore suitable for such fast fill or drain rates. By engineering the hydraulics of these high flow sensors a minimum lag between the sensor liquid annulus and bulk tank level (level reading Lag) is kept below 1 mm.


Integral Dewar Sensors - In dewars with very small volumes or all-attitude requirements it is especially advantageous to incor porate the level sensor into the dewar structure. Doing so provides only a single coax connection point on the outside of the dewar for connection back to the level instrument. 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.


Flow-Thru Style Sensors - For small dewar applications AMI utilizes a unique Flow-Thru sensor design that 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. These can be provided on dewars with a single port of 3/8" or larger. 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 smallest dewar volumes of less than 0.25 liters in size. Photo to right shows flow-thru sensor with integral venting.


Mini Dewar Flow-Thru Sensors ( < 1 to 0.1 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.


Modified Dewar Cap Assemblies - Dewar cap assemblies can be provided with in a variety of configurations which are adapted to allow autofilling for a particular application. These are available with foam neck plugs, stainless flanged versions or small nylon plug assemblies (some examples shown below). Simply contact AMI with the make and model of your dewar and let us handle the rest.





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