Partnering up for ACHEMA – OEM amperometric oxygen gas sensor modules and transmitters

OEM amperometric oxygen gas sensor modules and transmitters

Angst+Pfister Sensors and Power has over 150 different OEM amperometric oxygen gas sensor modules in our program, including many customer specific types. In this newsletter (Newsletter 2), we can merely scratch the surface of our vast product portfolio so-to-speak and we cannot go in detail with every single product. Many of the products shown in this newsletter, will only be mentioned with a brief statement of functionality or most popular application. Over 2/3 of our business within OEM oxygen gas sensor module business are customer specific modules. We consider ourselves oxygen gas sensor specialists and we are happy to work with customers and potential customers on customized solutions.

Generally speaking when developing an OEM oxygen gas sensor module based on the amperometric oxygen sensors presented in Newsletter 1, we strive to make a 1:1 transfer of the properties of the standalone amperometric oxygen sensors onto the OEM amperometric oxygen gas sensor modules, while adding some extra strong points/features to the product. These extra features could be integrated gas tight flow housings for fast, forced flow applications or high temperature sensor front end designs for easy integration into a given application.

We condition the sensor raw signal and amplify the raw signal into industry standard signal protocols, always having an eye on keeping the electronic noise from the electronics and surroundings at a minimum. Every electronic design is done with a focus on minimizing EMC problems and delivering a high quality output signal that is proportional to the oxygen concentration. In addition, every electronic design is done with a focus of protecting the raw sensor from interferences and transients.

FCX-M oxygen gas sensor modules based on the FCX-U amperometric oxygen sensors
The FCX-MC oxygen gas sensor module is the module for all. It has a 12-bit AD converter for conditioning and linearizing the raw signal from the FCX-U sensors. There are several output signal protocols available by using a FCX-MC module, namely 4-20 mA/0-10 V analog output and RS232/RS485 serial, digital output. The calibration and the adjustment of the signal is done using accurate digital potentiometers controlled by an external display box. In this way, the signal can be very accurately calibrated and adjusted in the application. The heater voltage to the FCX-U sensor is monitored and controlled and in case of a heater short circuit, a signal is being transmitted indicating an module error state. Likewise, the raw signal from the sensor can be monitored to be able to detect cable defects. The FCX-U sensor can be placed on the board in a gas tight flow housing for fast and reliable forced flow measurements or it can connected to the board via a cable. The maximal cable length is 6 meter, extendable to 10 meters depending on the application. There are several sensor heads in combination with cables available for different applications ranging from stationary, long-life gas safety devices to high-temperature humidity measurement transmitters. Some of the solutions are shown in the figure below, but again these are only a small part of what is available.

All of the different sensor head configurations and can cable types can also be combined with a ML/MP type of electronics. The ML/MP electronic has a more simple circuit design, but without compromising output signal quality and the heater voltage control. The output from a FCX-ML/MP oxygen gas sensor module is 4-20 mA, non-linearized. The calibration and the adjustment of the signal is done using normal, analog potentiometers. The ML/MP electronics has an advantage over the MC electronics in size, but also for some applications requiring a good performance in a narrow oxygen concentration band at higher oxygen concentration, the FCX-ML module is sometimes preferred over the FCX-MC module. For a FCX-ML95 module operating most of the time above 90 Vol%O2, the signal output increase per Vol%O2 is higher for a FCX-ML95 gas sensor module than it is for a FCX-MC95 gas sensor module with a linearized output.

The latest module development (FCX-MLD) is targeting long-life, low service oxygen gas sensing devices, for instance for applications in which the oxygen concentration in fitness rooms or in server facilities are lowered. These are two very different applications – in one application lowering the oxygen concentration simulates height training and in the another application lowering the oxygen concentration will slow down/prevent a fire breaking out, because of failed or overheated electronics and cables in a server room. Although, the applications are very different, the requirements are almost the same; stable, reliable output with low drift and long operational lifetime. The FCX-MLD oxygen gas sensor module is developed with focus not only on size, but also with focus on safe handling. The signal interface is serial and the commands for reading and writing are focused on safe handling; i.e. sensor/module status, sensor on/off, reset, span read/write and zero read/write along with other commands. The FCX-UC 0-25 Vol%O2 sensor is soldered onto the MLD print and the module works in a diffusion mode. By using the FCX-MLD module, the measured oxygen concentration can be controlled in a tolerance of +/- 0.1-0.2 Vol%O2 above 10 Vol%O2 absolute. The FCX-MLD95 oxygen gas sensor module is developed for retrofitting oxygen sensors into CO2 incubators and/or shakers or for integration into food packaging lines close to the actual packaging process.

FCX-TR oxygen gas sensor transmitters based on the FCX-U amperometric oxygen sensors
The FCX-TR oxygen gas transmitter has the advantage of having the FCX-U sensor and the electronics integrated into a stainless steel (1.4404) housing with a G½ threaded process adaption. The transmitter can thus be mounted directly in the application – be it in a tube or a in chamber and the signal conditioning is done directly. The output from the transmitter is 4-20 mA, non-linearized and there is no limit for how long the cable from a central process controller to the process-to-be-monitored can be.

The FCX-TR oxygen transmitters are developed mainly for process control in oxygen and nitrogen generators, but can also be used for analysis devices. The threaded process adaption make the integration easy, but the transmitter can also be operated in a forced flow mode. On the hexagonal nut there is threaded opening allowing for a M5 process adapter to be screw mounted and tightened. In this way the transmitter can be operated as a by-pass from the process gas line and the reaction to changes in the oxygen concentration is fast. 

PO2ES oxygen gas sensor modules
The PO2ES oxygen sensors can be used as standalone sensors in analyzers or gas safety devices. The output signal from the analog sensors is a passive temperature compensated, mV signal. Provided that the cable length is kept relatively short (< 30 cm), the mV output signal can be used directly. The output signal from the digital sensors is a temperature compensated, I2C signal with a very high resolution. The resolution can be as high as +/-20 ppm in a measurement range from 0 to 25 Vol%O2. A signal resolution of +/-1 ppm is guaranteed for the PO2ES sensor with the measurement range from 0 to 10.000 ppmO2.

The M16 x 1 mm threaded process adaption make the integration into the application easy, and for forced flow measurement we have developed a gas tight flow housing.

For many industrial applications the physical distance between a process chamber/process line and the central process controller (for instance a PLC) is long and many controllers cannot handle mV or I2C signal protocols. For such applications, we have developed a solution that convert (converter box) the direct signals from the PO2ES sensors into standard industrial signal protocols – in this case RS485 Modbus and 4-20 mA. The converter box can be mounted close to the measurement point of interest and from the converter box to the process controller the cable length has no limitation. The combination of a digital or analog PO2ES oxygen sensor with the converter has gained popularity in the additive manufacturing world of applications. The output signal PO2ES-103 has no influence (unlike other oxygen sensors) from the state of the process chamber and the gases that evolve during the build job – this could be reducing gases and/or humidity from the chamber walls and metal powder – and the signal resolution is high enough for build jobs with titanium and aluminum.

The latest development using the PO2ES sensors as basis, is the sensor combined with a datalogger. The sensor and the datalogger is connected with a cable (≤ 100 cm) and the datalogger is logging and storing the oxygen concentration in intervals between 1 measurement/second and up to one measurement every 12 hours. The communication with the datalogger is over a Bluetooth low energy (BLE) protocol. This product has been developed specifically for transport and storage of goods that need a protective/controlled atmosphere. This could be transport and storage of metal powder, milk powder or fruit and vegetables.

TB oxygen gas sensor modules based on the ES1-O2 amperometric oxygen sensor
The ES1-O2 0-25 Vol%O2 oxygen sensor need a conditioning electronics with a very stable reference voltage in order to deliver a stable output which is proportional to the oxygen concentration. The TB series of conditioning electronics is developed specifically for the ES1 series and has a lot to offer.

The TB200B-ES1-O2 digital board with the UART communication protocol has a very high signal resolution and a very good stability. The TB420-ES1-O2  analog board has 4-20 mA output and a very good output stability. Both modules have internal watchdogs for checking the state of the sensor and for reporting errors in the board electronics and in the sensor. The output signal is temperature and humidity compensated between -40°C and 55°C. The broad temperature range is very well suited for outside applications and for cold storage facilities.

The TB200B and TB420 footprint are very small (40x30 mm and 45x35 mm, respectively) and the module + sensor can thus be integrated into an application with a small head space volume. For instance in combination with the above mentioned datalogger.

The TB200B digital and the TB420 analog gas sensor modules are both a perfect match for small handheld analyzers. The output signal is independent of the sensor orientation and the sensor has no or very little cross influences from other gases such as, but limited to, carbon dioxide, carbon monoxide, methane, propane and hydrogen sulfide. For analyzers working with a pump and for applications, where only a very small head space volume is available for analysis, we have developed a gas tight flow housing for forced flow measurements.

If you have any questions, please do not hesitate to contact Peter Felder.