WHAT IS A PT100 PROBE?
He PT100 es un sensor de temperatura que a 0 °C tiene 100 ohms y que al aumentar la temperatura aumenta su resistencia eléctrica. Este sensor PT100 es el corazón sensible a la temperatura de cualquier termómetro de resistencia. Aparte de la forma de montaje, son sus características las que básicamente determinan las propiedades técnicas de medida del sensor.
Features of PT100 probes
El incremento de la resistencia de la sonda PT100 no es lineal pero si creciente y característico del platino de tal forma que mediante tablas es posible encontrar la temperatura exacta a la que corresponde. Normalmente las PT100 probes industriales se fabrican encapsuladas en la misma forma que los termopares, es decir dentro de un tubo de acero inoxidable u otro material (vaina).
At one end is the sensitive element (RTD Sensor) and at the other is the electrical terminal of the cables protected inside a round aluminum box (head).
Construction and operation
Depending on the construction method, the temperature-sensitive, wire-wound portion of the PT100 sensor, in the form of platinum wire or ribbon, is encapsulated in a ceramic or glass body, or is applied as a thin layer on a ceramic plate. The terminals of the measuring element are connected to the active resistive portion in a way that makes them resistant to vibrations.
In the case of multiple PT100s, the individual coils are identified by the different lengths of their terminal pairs. The operating principle of PT100s is the modification of their electrical resistance, which varies according to the temperature to which they are subjected. As an extended element, the PT100 measures the average temperature along its entire length.
Standards for our probes
All platinum PT100 sensors supplied and installed by SRC comply with the basic values and permissible deviations of DIN IEC 751. The DIN values apply to a nominal resistance of 100 ohms. The temperature stability of the PT100 sensor with respect to its measured values also meets or exceeds DIN IEC requirements.
Types and assemblies of PT100 probes
To obtain a reliable temperature measurement with a platinum PT100 sensor, its mechanical and technical characteristics (size, shape, vibration resistance, temperature range, response time, insulation resistance, etc.) must be suitable for the measurement class and the conditions of the application. The most standard models consist of a stainless steel protective tube in which the sensor is placed and which has an output via cable, connector, or header.
Aparte del rango de temperatura del PT100, el montaje determinara el rango de temperatura de la sonda PT100.
Apart from the need to select the appropriate PT100 model, mounting in the place where you want to measure is of special importance. This requires a high degree of knowledge, so we recommend the advice of our applications technician.
Advantages of PT100 probes
PT100s being slightly more expensive and mechanically not as rigid as thermocouples, outperform them especially in low temperature applications. (-100 to 200°). PT100 sensors can easily deliver accuracies of one tenth of a degree with the advantage that the PT100 does not break down gradually giving erroneous readings, but rather opens normally, whereupon the measuring device immediately detects sensor failure and gives warning.
This behavior is a great advantage in all types of devices where an undetected temperature deviation could cause some serious damage. In addition, the PT100 can be placed at a certain distance from the meter without much problem using conventional copper cable to make the extension. It will depend on the type of connection to minimize signal losses, we will show them below.
Precautions for use of PT100 probes
It is common in very humid environments for cables to deteriorate and for current to flow through them via condensed moisture. Even if it is minimal, this "leaked" current will make the reader display a lower temperature than it actually is. These leaks can also occur due to rust, moisture or dust covering the terminals.
From the description made of the measurement methods, it is clear that unlike thermocouples, it is not possible to connect 2 reading units to the same Pt100 since each one supplies its excitation current.
When purchasing a Pt100 sensor, it should be borne in mind that there are different qualities and prices for the sensor element that goes on the end of the Pt100 sensor. The best quality ones are made with a true platinum wire, while there are some cheap sensors made on the basis of a conductive paint on an alumina (ceramic) substrate. The latter are less accurate.
In general, a Pt100 should not be mounted in places subject to a lot of vibration as it is likely to fracture.
Connection for PT100 Probes
- PT 100 2-WIRE -
The easiest way to connect (but least recommended) is with just two cables. This is only recommended for measuring up to 10 meters from the temperature regulator since from there the pt100 sensor may have signal losses.
- PT 100 3-WIRE -
The 3-wire connection method is the most common and widely used for industrial processes, effectively resolving the problem of errors caused by cables. The only requirement is that all three wires have the same electrical resistance, as the measurement system is (almost always) based on the Wheatstone bridge. Naturally, the temperature sensor must be compatible with this type of connection. Most industrial equipment is designed for 3-wire connections.
- PT 100 4-WIRE -
The 4-wire method is the most accurate of all and is used in the laboratory. The 4 wires can be different (different resistance) but the reading instrument is more expensive.
DO YOU NEED A CUSTOM PT100 PROBE?
Send us your inquiry and our technical department will contact you as soon as possible.