Cryogenic Temperature Sensors

Cryogenic Temperature Sensors
Cryogenic Temperature Sensors

Cryogenic Temperature Sensors   

From near absolute to over one thousand degrees   

Lake Shore offer four types of sensor for cryogenic temperature measurement: diodes, resistors, capacitors and thermocouples. Each has its own particular features, so Elliot Scientific recommends contacting us to discuss your requirements and application.

Diodes
A diode temperature sensor is the general name for a class of semiconductor temperature sensors. They are based on the temperature dependence of the forward voltage drop across a p-n junction. The voltage change with temperature depends on the material. The most common is Silicon, but Gallium Arsenide (GaAs) and Gallium Aluminium Arsenide (GaAlAs) are also used.

Resistors
These sensors are based on the change of resistance with temperature, and can be classified as positive temperature coefficient (PTC) or negative temperature coefficient (NTC). Platinum RTDs are the best example of PTC resistance sensors.

The three most common NTC resistor materials are Cernox™, Germanium and Ruthenium Oxide (Rox™). Cernox™ is the trade name for the sputter-deposited zirconium oxy-nitride thin film resistor manufactured by Lake Shore Cryotronics. It delivers good temperature sensitivity over a wide range and is highly resistant to magnetic field-induced errors and ionising radiation. Cernox™ can come in the same robust hermetically sealed SD package that is used for diode temperature sensors, making Cernox™ more robust than other NTC RTDs.

Capacitors
Capacitors are also used for low temperatures, but usually not for temperature measurement. Capacitance temperature sensors have the advantage of being insensitive to magnetic fields, but they commonly experience calibration shifts after thermal cycling.

Symbol key
♨   Temperature range (K)
⌒   Standard curve response
❆   Operates below 1 K
☢   Radiation compatability
⋐   Magnetic field performance

Thermocouples
Thermocouples are only useful where differential temperature measurements or low mass are the main consideration. They must be calibrated in-situ as the entire length of the wire contributes to the output voltage if it traverses a temperature gradient.

Sensor overview

Capacitance

♨   1.4 to 290 ⌒   ✘ ❆   ✘ ☢   ✘ ⋐   ★★★


Capacitance sensors are ideally suited for use as temperature control sensors in strong magnetic fields because they exhibit virtually no magnetic field dependence. Small variations in the capacitance/temperature curves occur upon thermal cycling. It is recommended that temperature in zero field be measured with another cryogenic temperature sensor, and that the capacitance sensor be employed as a control element only.

Cernox™

♨   0.1 to 420 ⌒   ✘ ❆   ✔ ☢   ✔ ⋐   ★★★ (1 K +)


Cernox™ sensors can be used from 100 mK to 420 K with good sensitivity over the whole range. They have a low magnetoresistance, and are the best choice for applications with magnetic fields up to 30 T (for temperatures greater than 2 K). Cernox™ are resistant to ionising radiation, and are available in robust mounting packages and probes. Due to their versatility, they are used in a wide variety of cryogenic applications: particle accelerators, space satellites, MRI systems, cryogenic systems and research science.

⚠ These are sensitive to electro-static discharge. ESD precautions to be taken when handling them.

GaAlAs

♨   1.4 to 500 ⌒   ✘ ❆   ✘ ☢   ✘ ⋐   ★


GaAlAs Diodes offer high sensitivity over a wide range of use (1.4 K to 500 K). They are useful in moderate magnetic fields, and offer many of the advantages of Silicon Diodes. However, they do not follow a standard curve.

Germanium

♨   0.05 to 100 ⌒   ✘ ❆   ✔ ☢   ✔ ⋐   ✘


Germanium RTDs have the highest accuracy, reproducibility, and sensitivity from 0.05 K to 100 K. They are resistant to ionising radiation, but are not recommended for use in magnetic fields. Germanium RTDs are used mostly in research settings when the best accuracy and sensitivity are required. Germanium and Ruthenium Oxide are the only two cryogenic temperature sensors that can be used below 100 mK.

HR Series

♨   20 to 420 ⌒   ✘ ❆   ✘ ☢   ✔ ⋐   ★★★


The HR Series is a new line of high reliability cryogenic temperature sensors for mission-critical applications. Based on exisiting proven temperature sensor technology, Lake Shore has developed a family of off-the-shelf sensors that have already undergone extreme testing for the assurance of extra reliability.

Platinum

♨   14 to 873 ⌒   ✔ ❆   ✘ ☢   ✔ ⋐   ★ (30 K +)


Platinum RTDs are an industry standard and are used in many precision metrology applications. They follow a standard curve from 73 to 873 K with good sensitivity over the whole range, but can also be used down to 14 K. Unfortunatley, Platinum RTDs have limited packaging options, but are inexpensive and require simple instrumentation.

Ruthenium Oxide (Rox™)

♨   0.01 to 40 ⌒   ✔ ❆   ✔ ☢   ✔ ⋐   ★★ (< 1 K)


Ruthenium Oxide RTDs can be used to below 50 mK. Their unique advantage is that they have a low magnetoresistance and follow a standard curve. Their upper temperature range is limited to 40 K, so Cernox™ sensor are better suited in magnetic fields for temperatures above 2 K. Ruthenium Oxide sensors are used for applications such as MRI systems and, along with Germanium, they are the only cryogenic temperature sensors that can be used below 100 mK.

⚠ The RX-102B does not follow a standard response curve. It is not recommended for use in magnetic fields.

Silicon

♨   1.4 to 500 ⌒   ✔ ❆   ✘ ☢   ✘ ⋐   ★ (60 K +)


Silicon Diodes are the best choice for general-purpose cryogenic use. The cryogenic temperature sensors are interchangeable (they follow a standard curve) and are available in robust mounting packages and probes. Silicon Diodes are easy and inexpensive to instrument, and are used in a wide variety of cryogenic applications, such as cryo-coolers, laboratory cryogenics, cryo-gas production and space satellites.

⚠ These are sensitive to electro-static discharge. ESD precautions to be taken when handling them.

Thermocouples

♨   1.2 to 1543 ⌒   ✔ ❆   ✘ ☢   ✘ ⋐   ★


Thermocouples can be used over an extremely wide range and in harsh environmental conditions. They follow a standard response curve but are less accurate than other cryogenic temperature sensors. Special techniques must be employed when using thermocouples to realise temperature accuracies of 1% of temperature. Their small size, extremely wide temperature range (exceeding the high temperature limits of Platinum RTDs), and simple temperature measurement methodology make thermocouples ideal in many applications.

Cryogenic accessories

Wire
Specially engineered cryogenic wire is often used to minimise heat transfer into the sensor and cryogenic system. It has a much lower thermal conductivity (and higher electrical resistivity) than copper, and is available in one-, two-, and four-lead configurations.

Four-lead configurations are available as Quad-twist™ (two twisted pairs) or Quad-lead™ (ribbon). The wire is 32 or 36 AWG, with polyimide or polyvinyl formal (Formvar®) for insulation.

Epoxy
For sensor installation and fastening to the sample, epoxies provide good thermal contact and electrical insulation.

Lake Shore offers Stycast® 2850FT, a black epoxy resin with a thermal expansion coefficient matched to copper; or ESF, a silver-filled low-temperature conducting epoxy that provides excellent strength, along with electrical and thermal conductivity.

Bobbins and holders
Heat sink bobbins, a beryllium oxide heat sink chip, and a four-lead resistance sample holder can be supplied by Lake Shore, along with cartridge heaters and vacuum feedthrough products. Please contact us for details.

Product Code: Lake Shore Cryosensors

Availability: Contact us for details
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