Thin-film RTDs are platinum elements that are constructed by placing a sensing platinum layer over a ceramic substrate, covered with passivation glass layers. This results in excellent shock and vibration resistance and protects the Pt sensor element from environmental influences.
The platinum wire of a ceramic wire-wound Pt100 sensor is wound into a small coil that is inserted into the holes of a high purity alumina tube. The outside diameter of these high purity alumina tube varies from 0.8 mm to 4.5 mm, so they are even suitable for the thinnest RTD mineral insulated cables.
What RTD sensor do you need?
Choosing an RTD sensor like thin film or ceramic wire wound depends on the following things:
- Temperature range
- Nominal resistance
- Dimensions
- Costs
The most important one is the temperature range. Depending on the temperature range one could determine what the preferred option will be: Thin film, ceramic wire wound or SMD platinum Pt element.
Temperature range RTD sensors
Ceramic Wire Wound
A ceramic resistor generally has the widest temperature range in combination with the narrowest tolerances for higher temperatures. It can measure high temperatures due to the insulating material covering the platinum wires. However, they are not the best option for high frequency. In case of high frequency, the platinum wires can break after being exposed to high frequency for a long period of time.
Read more about ceramic wire wound.
Thin Film sensors temperature range
A thin film resistor generally has a wide temperature range, but is mostly available in class A up to ± 300°C. A thin film resistor can withstand environments with high vibration well.
| Element type | Operating temperature | Lead wire material | Recommended connection method |
|---|---|---|---|
| C | -196 to +150°C | AgPd | soft soldering |
| L/LN | -50 to +400°C | AgPd — silver coated Nickel | soft soldering |
| M | -70 to +500°C | Ni/Pt | hard soldering, welding, crimping |
| HM | -70 to +600°C | PtPd | hard soldering, welding |
| HL | -70 to +750°C | Pt/NiCr | hard soldering, welding |
| HD | -70 to +850°C | Pt | hard soldering, welding |
Source: Yageo Nexensos GmbH
Read more about Thin Film elements
Platinum Surface Mount Devices (SMD)
SMD platinum elements are perfect for being mounted on a printed circuit board. The SMD’s have a linear temperature coefficient of 3850 ppm/K and are operational within a temperature range of -50 °C up to +150 °C.
Read more about Surface Mount Devices
And the other factors?
When comparing the Pt100 versus Pt1000 in terms of resistance, keep in mind that resistance value readings for the Pt1000 will be higher by a factor of ten than resistance value readings for the Pt100 at the same temperature. For most applications, the Pt100 and Pt1000 can be used interchangeably depending on the instrument used. In some cases the Pt1000 will work better and be more accurate.
In case of a 2-wire configuration, one could prefer a Pt1000 over a Pt100 since the measurement error of a Pt1000 will be lower.
Dimensions
Moreover, the dimensions of a Pt element are of great importance.
The alumina tubes of ceramic wire wound come with outside diameter (OD) that vary from 0.8mm to 4.5mm so they are even suitable for the thinnest mineral insulated RTD cables.
Thin film elements come in different sizes. Thin film elements can be as small as 1.0 mm, they could fit in the very thin tubes. The following table summarizes some size dependent properties;
| Smaller element | Larger element |
| Faster response time | Higher source currents possible |
| Higher self-heating constant | Lower self-heating constant |
| Self-heats at lower power | Requires higher power to self-heat |
| Fits in small ID sensor housings | Larger contact area for surface mounting |
SMD’s continue to become increasingly compact and the small SMD sizes we supply perfectly match this trend. Kamet currently offers the following dimensions:
| Product part number | Size (L x W x H in mm) |
| SMD 0603 | 1.7 x 0.9 x 0.45 |
| SMD 0805 | 2.3 x 1.4 x 0.6 |
| SMD-FC 0805 | 2.1 x 1.35 x 0.4 |
| SMD 1206 | 3.2 x 1.6 x 0.6 |
Yageo Nexensos also developed the micro RTD with the dimensions 0.6 mm by 0.3 mm. Please contact us for more information about this tiny SMD.
Cost of RTD elements
Lastly, costs are crucial when selecting a certain type of pt element. Ceramic wire-wound elements tend to be more expensive since a great part of the manufacturing process is still done manually. Thin-film elements being the most economical of the three options.
To summarize: Thin Film versus Ceramic Wire wound
The following table summarizes the advantages of each type:
| Thin-Film Element Advantages | Ceramic Wire wound Element Advantages |
| Low-cost | Higher source currents possible |
| Fast response time | Lower self-heating constant |
| Low thermal mass | Wider operating temperature range |
| High vibration resistance | Wider tight tolerance temperature range |
| High thermal shock resistance | Customizable R0 values |
| Small size footprint | Larger diameter lead wires |
Our RTD products
Check out our Thin film Pt100 elements product page
Check out our SMD Pt100 sensors product page
Check out our Ceramic wire wound RTD sensors product page