5
1
Introduction
1.1
Use of this Manual
This manual provides operating and service information for the Oxford Instruments
ILM200 Family of Cryogen Level Meters. Sections 1-4 provide essential information and
should be read before operating the instrument for the first time.
The remainder of the manual provides more detail on specific aspects and may be
referred to as required. Section 11 attempts to identify some of the more common
operating pitfalls and may be useful if problems are encountered.
A Quick Reference guide is provided in Section 13 to help to remind you of the
commands and configuration parameters. Please feel free to copy this and keep a copy
beside the instrument if you wish.
1.2
Description of the ILM
200
Family
ILM200 is a family of Intelligent Cryogen Level Meters with general application in systems
containing liquid helium or liquid nitrogen. The family comprises five instruments. The
last two digits of the type number specify the number of helium and nitrogen channels
respectively. Thus ILM221 is a three channel instrument with two helium channels and
one nitrogen channel. From now on, we shall use “ILM” to represent any member of the
family.
ILM uses a superconductive wire probe to measure the depth of liquid helium and a
capacitance probe to measure the depth of liquid nitrogen. ILM can have up to three
measurement channels, with dedicated displays used for each channel.
ILM is microprocessor based and incorporates all the logic needed to control an
automatic filling operation or to de-energise a magnet safely should the cryogen level
fall below a safe value. All members of the family include an RS232 Serial Computer
Interface as standard and if required may be fitted with an optional GPIB (IEEE-488)
Interface.
Manual operation of the ILM is by means of front panel push buttons and associated
status lamps.
1.3
Principles of Operation
1.3.1
Helium Level Probe
The probe consists of a length of superconductive wire extending from the bottom to the
top of the helium reservoir. Normally the probe will be mounted vertically, though other
geometries are possible to suit individual shapes of reservoir.
