Pressure and temperature sensors - second to none reliability

Saturday, 19 June 2010

Danfoss market temperature sensors and pressure transmitters for refrigeration and air conditioning for more than four decades and has captured market leader's position for almost the same period of time. Establishing production near our customers in Asia in parallel with the European sites stands up for this position in the years to come.

Chapter 1. Pressure and temperature sensors, second to none reliability

The secret behind this long lasting success is a combination of having quality sensors fulfilling customer demands and a stable group of sparring partner customers for product development. Seen through today's lenses one could say that the secret is that all the AKS sensors are striking examples for essentials like Customer Quality Experience and Bold Innovation. Customer's demands for accurate regulation, energy reduction and temperature documentation throughout the entire chain are tasks that can performed only with sensors that perform as or above the AKS series.

Chapter 2. AKS pressure transmitters

Originally, pressure transmitters were regarded in much the same way as pressure controls. They were installed in control cabinets and connected via capillary or steel tubes to protected environments but far from a position ensuring optimum control accuracy. The refrigeration industry demanded transmitters that could be installed precisely at the point where the pressure should be measured, as here the pressure signal is most correct, and they demanded pressure transmitters that were capable to resist moisture, ice formation, temperature variations, pressure pulsation, and vibration. This was the long lasting foundation when Danfoss developed the AKS pressure transmitters on which you may put four key design criteria:

1.Laser welding
2.Piezo Resistive Silicon measuring cells
3.Temperature compensation
4.EMC protection

Laser welding has the advantage that the transmitter is and remains hermetically sealed, irrespective of the refrigeration medium, temperature and age. All laser-welded joints are subjected to helium leak detection and the user is thus guaranteed a 100% hermetically sealed product.

Silicon has outstanding strength properties and is thus the best choice for our applications as it maintains it's original performance at high and low pressures and at high and low temperatures.

The temperature compensation is performed so that the signal from the pressure transmitter is most accurate within the working temperature range. Hence, transmitters for suction pressure regulation are optimised for working temperatures from -30o to +40oC whereas sensors controlling oil and discharge pressure are optimised for working temperatures from 0o to +80oC.

EMC protection is an area in which Danfoss never made compromises and over the years legislative demands to EMC have been ever increasing. Integrated circuits and full metal housing encapsulation make AKS pressure transmitters fulfil the international standards on both emission and immunity.

AKS pressure transmitters come with output signals like 4-20 mA and 1-5 V dc. However, the majority is with the ratiometric 0.5-4.5 V dc signal. Reason is not only that this is the less expensive sensor but highly that the total cost of ownership is lowest as the supply is 5 V dc. which means that a separate 12 or 24 Volt power supply is not necessary. Further you don't need a protection against over-voltage and the accuracy is better than with 4-20mA or absolute voltage signals.

Chapter 3. AKS temperature sensors

Often our pressure and temperature sensors goes hand in hand when considering supermarket applications, however in other customer segments the two types of sensors got their independent market position.

The AKS temperature sensors all have standardized Pt 1000 signal with class B accuracy. Also the less accurate NTC and PTC sensor from the EKS series are available; however this group of sensors are not covered by this article.

Most often the performance of large refrigeration installation relies on the signals coming from the temperature sensor why one should not compromise when selecting temperature sensors. Like with pressure transmitters the demands put forward from the refrigeration industry that the sensors must be suitable to last for many years in presence of moisture, ice formation, temperature variations, and vibration, have led to the high quality level and dictating the key design criteria: Tightness.

The families AKS11, AKS12 and AKS21 all have their individual market position based in various applications. To evaluate which sensor for what application you must pair product features with application requirements in order to serve your customer best. Below illustrations gives you an overview of the most common applications linked to some general requirements and guides you to the optimum temperature sensor choice.

Chapter 4. Conclusion

The world of today is driven by cutting costs and as a marketer you can't neglect this fact. Switching to a new supplier should bring you in a better cost position, regardless you have cost, quality or logistical problems with the current supplier. However, with sensors the minor part of the costs are the purchase - the major part is related the performance over years of operation. This was the essence of Danfoss' value proposition as an electronic controls manufacturer with the unique skills: Combining refrigeration know-how; system optimization and adaptive control skills with a robust packaging and design all this into our sensors.

The present market leader position is a proof for this strategy being right. Often customers tell that they like to work with Danfoss because they know our excellent quality; because we manufacture in Asia; because they rely Danfoss is a stable partner for a long future - in other words Danfoss does not live-and-die with the ups and downs of individual customers, but stands behind the products.