The popular Helium Depth Indicator  (HDI) is a helium level meter with a high Specification which can be added to with a series of options.  The basic unit allows for the full configuration of the unit via the front panel controls, or via the included Serial interface.

A brochure for the HDI in Acrobat pdf format can also be downloaded.

With suitable front panel configuration, the unit will also operate Twickenham's Nitrogen level gauge probe, and in that configuration it is operating auto-filling systems for liquid Nitrogen and liquid Argon in a number of industrial and research environments.

Each unit is supplied with one factory configured Analogue output, with a choice of three types:

In addition, from autumn 2002, the specification of the probe range that the unit is set up for is included in the product code. The probe range is the precise type of superconducting element used in that particular probe. It is normally a few minutes work to convert from one range to the other, and details are given in the product manual.

More details about probe ranges from the probe specification pages.

The HDI is specified as

HDI-[Analogue output][Probe range]...[Option 1][Option 2].....

The first two characters after the hyphen are always present, options are only included when they are needed.

The Options are specified as follows:

The HDI with its helium probes have been installed in a large range of systems from small research cryostats, storage vessels, liquefier systems to industrial scale equipment.  A few examples of installations:

Control of a liquefier system which fills up to three vessels (each with its own probe) from a selection of vessels, from one liquefier; the system has to identify which cryostat is attached (which it identifies from the probe) and provide the correct signals for when the vessel is full.

Monitoring of the helium level in large, body-scanner size magnets, and providing alarm signals once the level drops below a preset alarm level, allowing the system to de-energise without risk of quenching the magnet.

Notes for existing customers.

HDI unit running with firmware version 2.0 or higher can be upgraded to work with the current firmware, currently version 5.3.  While this will increase the functionality, not all facilities of the firmware will be available if certain options are not installed within the unit.

In the last few years, parts that were options have become standard. These include the backlit display and the Serial port. When options have become standard, the "option" has been withdrawn (except for hardware upgrades). The increase in specification of the unit has been done with no change in the price of the unit.

Unfortunately for nomenclature, the old Serial port option and the probe range character have to share the same letter; but the Serial port option was withdrawn many years ago, when it became standard, so there should be no confusion over the issue. Some further details are given in the Helium probe section

Twickenham Scientific Instruments Ltd.  Registered in England No. 2991094
Registered Office:  61d St. Margaret's Road, Twickenham, Middlesex. TW1 2LL, UK.
Telephone: +44 20 8892 7400