changes the rules 1. What oxygen technology is used in ventilators and neonatal incubators?
Where oxygen measurement has been required in critical care ventilators and neonatal incubators, manufacturers have preferred to use electrochemical sensors. Electrochemical technology is now well established, its low cost appearing to outweigh its numerous performance issues. In particular, its short life has produced a sizeable after-market for replacement sensors.
Paramagnetic oxygen sensors offer considerable advantages over electrochemical sensors. Until recently, the high cost of paramagnetic technology has limited its use to high-end anaesthesia gas monitors. The new Paracube® has made paramagnetic technology accessible to those applications where the low cost of ownership of equipment is an important factor.
We hear the same story from both the nurses who use critical care ventilators and neonatal incubators and the technicians who have to service this equipment. The main issues with electrochemical sensors have been identified as:
A short and variable operating life disrupting the planned maintenance schedule
The need to freqeuently calibrate the sensor disrupting the continuity of patient care
The need to replace sensors regularly and keeping spare sensors in inventory adding to costs
The short shelf life making inventory management more difficult
The recovery from exposure to high oxygen concentrations is slow
A short and variable operating life…….
The electrolyte in the electrochemical sensor is consumed by the oxygen being
measured. The sensor will stop working correctly when the electrolyte is nearly
depleted. The depletion is accelerated by exposure to high concentrations
of oxygen and temperatures in excess of room temperature.
The Paracube® does not use consumable or depleting materials in its construction. This means its life will match that of the equipment it is installed in.
The need to calibrate frequently……
The characteristics of the electrolyte and the materials of construction of the electrochemical sensor change significantly with temperature, humidity, and duration of exposure to oxygen. This means that a daily calibration procedure is required, which includes exposure of the sensor to air. Not only are frequent calibrations time-consuming, but they increase the opportunity for an error to be made.
The Paracube® design and construction from high stability materials provide excellent long term drift performance. This means that the Paracube® does not have to be calibrated as frequently as the electrochemical sensor.
The need to replace sensors regularly and keep spare sensors in inventory….
The process of oxygen consumption of the electrolyte in the electrochemical sensor continues whilst the sensor is kept in storage. For this reason, every sealed sensor has a "use by date" stamped on the package. The sensors must be rigorously installed on a "first-in, first-out" basis, and care has to be taken not to install an expired sensor.
The Paracube® does not deplete so there is no need to stock spare sensors, saving on purchase cost and reducing the management burden.
The recovery from exposure to high oxygen concentrations is slow…
The electrolyte in electrochemical sensors saturates when exposed to high concentrations of oxygen. This means that the sensor output will continue to read high after the oxygen concentration is reduced.
The Paracube® does not use an electrolyte and so does not exhibit this behaviour.
The cost of a single Paracube® sensor is greater than that of an electrochemical sensor. This will certainly be reflected in the purchase price of new equipment. However, there will be no further costs of ownership associated with the oxygen measurement for Paracube®-fitted equipment.
On the other hand, there is a significant cost of ownership for equipment fitted with electrochemical oxygen sensors. There is the cost of the replacement sensors, at the rate of one or more per year for each ventilator and neonatal incubator. Other costs incurred include the disposal of the toxic material in depleted sensors, the management of the frequent calibrations and possible sensor failure during usage, and the management of an acceptable level of inventory for spare sensors.
The Paracube® is a non-depleting sensor that uses the innovative and patented Servomex resonator paramagnetic technology to provide a measure of the partial pressure of oxygen in a sample gas.
The Servomex resonator technology is a new and patented application of the magneto-dynamic paramagnetic principle. It takes advantage of the affinity that oxygen has for a magnetic field.
Servomex resonator technology applies the same fundamental magneto-dynamic paramagnetic principles as the reputable Servomex torque balance transducers. The innovative resonator approach allows a smaller device to be manufactured, whilst offering the well-established benefits of the Servomex paramagnetic technology - excellent stability and repeatability, and a long life.
Servomex resonator paramagnetic technology provides a superior performance and longevity, and a lower lifetime cost of ownership compared with the electrochemical sensor.
The Paracube® and the electrochemical sensor are both diffusion devices that offer comparable t90 step response times. However, unlike an electrochemical sensor, the response and recovery times of the Paracube® are not affected by an ageing process.
The electrochemical sensor is a fuel cell, producing an amperometric output. It requires a separate electronic circuit and power supply to provide a bias current and process the signal. The Paracube® is a digital device that requires only a +5V supply. It offers a standard UART output, making it easy to interface with most digital equipment.
The electrolyte in the electrochemical sensor is consumed when exposed to oxygen, and is liable to dry when exposed to elevated temperatures. This makes the lifetime of the electrochemical sensor difficult to predict, and causes the sensor to drift. The Paracube® uses no depleting or consumable materials in its construction. Its lifetime will match that of the equipment it is installed in, and its output will exhibit less drift.
Tests show that the t10-90 and t90-99 response times of the Paracube® to be better than 12 seconds and 25 seconds respectively.
The typical electrochemical sensor offers a slower response, particularly for the t90-99 figure. Some electrochemical sensors are designed to offer a very fast response. However, this is achieved by reducing the electrolyte volume, resulting in a significantly reduced sensor life.
No. Unlike an electrochemical sensor, the Paracube® does not take time to recover from exposure to high concentrations of oxygen.
At constant temperature, the Paracube® will stabilise within seconds of power being applied. Many electrochemical sensors take 4 to 8 hours to stabilise after the bias is applied across the electrodes.
Unlike the electrochemical sensor, there is nothing in the Paracube® that will deplete. The Paracube® will last as long as the equipment it is installed in.
The electrochemical sensor must be put into service before its use-by-date. The Paracube® has no use-by-date, and can be kept in storage indefinitely.
The Paracube® is not affected by non-condensing humidity. The electrolyte in electrochemical sensors, on the other hand, is generally hygroscopic. This means that the amount of water in the electrolyte tends to reach equilibrium with that in the sample gas. Therefore, a very hot and dry environment will reduce the life of an electrochemical sensor, as will a very high humidity.
Significantly less than with an electrochemical sensor. The design and materials selection for the Paracube® produces a long term drift performance, under constant conditions, of better than ±0.2% oxygen a week.
Passing fast-flowing gas across the face of the Paracube® can produce a marginal improvement in the response time of the Paracube®. Under the same conditions, an electrochemical sensor can dry out more rapidly than normal, reducing its life.
The Paracube® offers a lower cost of ownership than that of the electrochemical sensor. The Paracube® does not require replacing, and needs fewer calibrations.
The lifetime of a typical electrochemical sensor is reduced by exposure to oxygen and elevated temperature. Its performance will degrade over time, and the output of the sensor can drift significantly over the course of even a day. This means that the electrochemical sensor must be replaced several times during the lifetime of the equipment, and needs frequent calibration.
The lifetime of the Paracube® is independent of factors such as the oxygen concentration and operating temperature. Its high stability reduces the need to calibrate frequently, and there is no deterioration of its performance throughout the lifetime of the equipment.
The Paracube® is intended for use in medical applications and selected industrial applications where the sample gas is either clean oxygen or air. Its high performance and stability make it better suited than the electrochemical sensor for the monitoring and control of oxygen in equipment such as intensive care ventilators and neonatal incubators.
"Fit and forget" means that Paracube® can be installed in the factory, and apart from normal calibration, there is no requirement to service or replace the Paracube® at a later date.
The Paracube® fits into the space envelope 31mm x 35mm x 35mm, approximately the same size as a typical electrochemical sensor, making it the smallest paramagnetic transducer currently available.
A +5V supply capable of providing a 50mA current.
The Paracube® and the electrochemical sensor are diffusion devices of comparable size. Both sensors can therefore take advantage of the same, simple sampling system.
Normally, suitable filtering is designed into the sampling system. The Paracube® may be supplied with an optional 1µm filter fitted into the diffusion port. A fitted filter will result in a small reduction in speed of response.
Our experience shows that some help is needed during the development phase of a programme. We provide technical information on our technologies and products on the web-site "Servomex.com". Specific design and implementation enquiries will be handled our Customer Applications department, co-ordinated by your Key Account Manager.
Servomex has been designing and manufacturing innovative gas analysis solutions for over 40 years. The company's reputation in the medical market is built on an installed product base of over 45,000 paramagnetic, infrared and zirconia sensors with many leading medical equipment manufacturers.
Servomex has a policy of continuous product improvement. This means that its people are always seeking to improve product performance and reduce cost through innovation in product design, materials technology and manufacturing techniques.
Servomex Transducers is a business unit of Servomex Group Ltd, which is accredited to ISO 9001. The company is regularly audited by the British Standards Institute, and was one of the first companies in the UK to earn the original BS5750 accreditation in 1987.