Physitemp's miniature Type T thermocouple sensors provide the wide stand most versatile selection of temperature probes available for bioscience and analytical chemistry applications. All clinical probes and microprobes are made with Physitemp's proprietary copper-constantan thermocouple wire and are guaranteed accurate to 0.1°C within the physiological range. All probes are interchangeable and do not require individual calibration when used with any of our Type T thermocouple instruments.
Physitemp's tiny sensors, welded under microscopes, are used to make needle probes as small as 29 gauge and flexible probes with a diameter of .005". Small mass results in fast response times, with time constants as low as .005 seconds.
Physitemp's best selling probes, the flexible 1T- 18 series, are used in many scientific and industrial applications; for implantation in tissue, in spectrophotometer cuvettes, rectally in neonatal mice, and in water baths. They are fast reading, strong, completely sealed in flexible Teflon® and may be sterilized by gas (ETO) or autoclave.
Stainless steel needle probes as small as .033mm diameter are available. There are surface probes, animal rectal probes in several sizes, heavy duty probes and a wide range of clinical probes. Physitemp also make custom probes in any quantity including multisensor microprobes with as many as 10 sensors.
High accuracy is guaranteed
Physitemp specializes in the manufacture of Type T (copper-constantan) thermocouples. Small, flexible sensors are in demand for use in medical applications where high accuracy and interchangeability are required. Type T wire is widely recognized as being the most suitable thermocouple for these applications.
Accuracy of ±0.1 °C in the physiological range is possible and the probes are completely interchangeable. Wire with only ±0.5 °C accuracy is readily available. This is known as "Special Limits" wire. Physitemp is a supplier of the premium grade with accuracy to 0.1 °C.
Advantages of Thermocouples
There are currently six different common techniques for measuring temperature : thermal expansion, such as the bimetallic strip or liquid-in-glass thermometers, bulk resistance devices such as platinum RTD's and thermistors, semiconductor devices including diodes and transistors, thermocouples, liquid crystals and infrared noncontact devices. Of all the contact measurements techniques listed above the thermocouple is the smallest in size, fastest responding and lowest cost. This offers the least perturbation to the object being measured, and hence, the most accurate interpretation of its temperature. Their wide operating range and low relative cost make thermocouples ideal for most bioscience and industrial applications.
What are thermocouples ?
A thermocouple is a junction of two dissimilar metals and exhibits galvanic activity in response to a temperature gradient across the junction. Many conductors exhibit this effect, however in practice only eight or nine different types of thermocouples are used extensively in a vast array of industrial, commercial, medical and research applications. Selection of a thermocouple e for a specific application is related to cost, temperature range, accuracy, stability and operational life expectancy.
A thermocouple sensor is created wherever the wires comprised of the two dissimilar metals are joined together electrically.
The junction is usually a welded connection because this minimizes the size of the junction and provides the fastest response time. In addition, because the weld melts at such a high temperature it enable s the probe to be used over a much wider temperature range. The sensor may also be formed by soldering or crimping, neither of which will affect the accuracy of the junction in measuring temperature although the response time may be slower and the melting point and corrosion resistance of the sensor junction may suffer when soldered. Since most of Physitemp's thermocouples are made under a microscope, the quality and consistency of each weld is very high.
Isolated vs. Non-isolated
In a non-isolated sensor, the thermocouple bead is in direct contact with the object being measured, or it is in electrical contact with an outer and electrically conductive sheath that is in contact with the object. The advantage of the non-isolated sensor is the improved response time in both the sheathed and unsheathed forms.
An isolated sensor may be needed in an electrical application or one in which more than one sensor is present in a conductive medium. If the object being measured is electrically conductive and at an elevated potential, it is especially important in order to prevent an electric shock to the operator or damage to the measuring instrument.
In many medical applications invasive sensors may be in contact with internal body fluids which are comprised of conductive electrolytes. Isolated sensors are required in these applications to avoid galvanic interaction between temperature sensors and other types of electrical sensors such as EKG electrodes.