A brochure for helium probes in
pdf format can be downloaded.
Each probe is made to customer order, and its part number describes all the required
details. There are six fields in the part number, which has the general form:
MR-TL-AL-CN-NN [option codes]
Each of these codes have a meaning as described here: All dimensions are expressed
in millimeters, except where stated.
- MR. This consists of two single letter codes, which specifies the probe series and
range. The probe series (M) is based upon the physical construction of the probe, with the three
most frequently specified are:
- Stainless steel tube (Sx)
- pultruded Glass Fibre (Gx)
- PTFE/Teflon (Px)
In addition, there is a variant of the Sx range, Rx, which is a radiation-hard version.
A range using Polyetheretherketone (PEEK) tubing, to be labelled Kx, is being developed.
The probe range (R) specifies the type of superconducting element that is used in the probe.
The original probe range, xS, was supplimented by a new range, xG, in 2001. At that time, this
change in nomenclature was introduced to the probe part number. In autumn 2002, the
probe range is also specified in the product code number of the Helium Depth
Indicator.
A small number of product code changes have been necessitated by this; these are given in the
Changes section.
- TL This is the total length of the probe.
The total length is defined by the way the probe is installed.
- For probes which run from the helium and out of the cryostat, the total length is from
the bottom to the pinch seal, or other point where the probe is sealed to prevent the
atmosphere entering. Details about the type of connector, or type of fitting do not
affect the definition of the total length.
- For probes which are installed within the cryostat, and have wires running from the
probe up to a user supplied feedthrough, the total length is the entire length of the probe,
including any special terminations for the wires into the probe.
- AL The active length, that is the length of the superconducting element of the probe
- CN The type of connector or wiring. The standard is a 7 pin male (7M); which
allows for connection to the Helium Depth Indicator.
Other types of connector can and have been used, with a different code to identify them.
Alternatively, a simple number indicates the wire length for a wire ended probe.
- NN The diameter of the main section of the probe, expressed in tenths of millimeters
(so 21 = 2.1mm) The standard diameter for SS range probes is 2.1mm
- Option codes The following is a short list of the more
frequently specified options. either alone, or in some allowed combinations Other
designs and types can be accommodated
- T For wire ended probes, this specifies that colour coded Teflon insulated
copper-nickel alloy wires are to be used
- D The venting holes at double the standard frequency, i.e. 25mm instead of 50mm
- PW & SW Two types of integral still well to be built around the probe as one
complete item, for use in dewars attached to liquefier systems, for example. The
minimum outside diameter for a still well probe (the diameter NN) is 4.0mm
- /rr(WL) Defines a larger diameter collar (of diameter r.r mm, and length WL) at the top
of the probe, to allow the probe to seal into an existing (larger) port on a cryostat with a
separate adaptor
- Special probes Twickenham has more than twenty years of manufacturing
helium probes to special designs. As these may be one-off designs to match
customers requirements, or to overcome some limitation. It may be the case that
it is not possible to describe the one off feature within the normal nomenclature, so
the normal probe description would be used, and a Special Probe (SP) number assigned
to the project. The types of special features include
- Connectors. While the probe part number will have to describe the connector,
for example the number of pins, a code to describe the connector in some way, a SP number
may be needed to describe the way that the connector is fitted to the probe.
- Probe shape. Probes with preformed curves, or the connector mounted at
an angle to the probe tubing are typical examples
Changes
Due to the change in nomenclature necessitated by product improvements, there are a few cases
where a product code has had to change. The changes are summarised here. The examples given
here are where a code has been used in the past, but to specify the same unit with the change, a
part code has to be changed. Other possible codes which were never required to be specified before
are not listed here.
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Glass fibre tubing for probe, original superconducting element |
Product code starts GF- |
Product code starts GS- |
Tufnol tubing for helium probes |
Product code starts TF- |
Series withdrawn due to poor available tubing |
PTFE/Teflon tubing for probe, original superconducting element |
Product code starts PF- |
Product code starts PS- |
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HDI with Serial port option (up to 1997) |
HDI-xS [O1]... |
HDI-x [O1]... |
HDI calibrated for original superconducting element (from autumn 2002) |
HDI-x [O1]... |
HDI-xS [O1]... |
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
Email: sales@twicksci.co.uk