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At Sentron, we develop and produce sensors in our inhouse semiconductor production facility. Through many years of experience and specific know-how for die attaching, wire bonding, encapsulating, steering and compensating sensors, we also design and manufacture sensor assemblies and complete products with our pH and pressure sensors as well as with third party sensors.

More info

At Sentron, we develop and produce sensors in our inhouse semiconductor production facility. Through many years of experience and specific know-how for die attaching, wire bonding, encapsulating, steering and compensating sensors, we also design and manufacture sensor assemblies and complete products with our pH and pressure sensors as well as with third party sensors.

ISFET: robust, dry storage

Our comprehensive line of high-quality probes for glass-free pH measurements is created for Sentron’s proprietary ISFET (ion-sensitive field-effect transistor). Because of the ISFET technology the sensor probes are robust and can be stored dry, which makes them well suited for e.g. agri- and horticulture, inline food processes, laboratory use, outdoor water measurements and medical applications like gastro-enterology.

ISFET in theory

The pH is a widely used way of expressing the acidity or alkalinity of aqueous solutions. In essence it is a means of indicating the hydrogen ion (H+) activity in products, which in turn is the direct availability of free H+. The commonly used pH scale is from 0 to 14: a pH value of 7 is neutral, values below 7 are acidic and those above 7 are alkaline or basic.
Mathematically, the pH is expressed as pH = -10log (aH+), where aH+ is the hydrogen ion activity. Hydrogen ions are made available (i.e. free) by the ability to dissociate from their parent compound. Strong acids like sulfuric acid, H2SO4, and weak acids like boric acid, H3BO3, both contain H+, but the H+ in strong acids dissociates in the presence of water to become free H+. In weak acids, when added to water, very little of the hydrogen is liberated as free H+. Instead it remains relatively inert in the undissociated molecules of the acid. Thus, other than expressed as concentration or strength, the pH expressed as hydrogen ion activity is a more precise way to know about the quality or effectiveness of water-based products.

The principle of the ISFET technology is that when the H+ activity changes, the current driven voltage will change and a different pH value is measured accordingly. To complete the electrical circuit, the ISFET sensor (also called the indicator electrode) needs a reference electrode. For any change in the analyte concentration, the potential of the reference electrode will remain virtually constant and so the change of potential will only be caused by the indicator electrode. Sentron has a broad experience in the development and manufacture for the circuitry and reference electrodes and owns tiny, stable designs compatible with medical and food safety standards.

ISFET in practice

Fast, reproducible results are easily achieved as long as good contact between the sample, the ISFET sensor and the reference electrode diaphragm is made. Also, for testing thick or viscous samples the probes are suitable, although it requires a little stirring of the sample with the pH probe or placing the sample material directly onto the probe tip.

The method by which ISFET sensors and glass bulb pH electrodes achieve a response is significantly different. In buffers and most samples, the pH value based on both technologies will be the same. However, differences due to method may occur in applications like milk and cheese. As these are reproducible readings, the bias can be set in the pH meters to come to the same readings as the glass electrodes. The reason for different outcomes is primarily the following. Glass bulb electrodes use a permeable glass membrane involving an ion exchange process. The pH value measured by glass electrodes is based on the H+ concentration. Instead, ISFET sensors use an instantaneous surface reaction. The pH value measured by ISFET electrodes is based on the H+ activity, as described above.

Full wheatstone bridge pressure sensors

In our facility we produce the advanced miniature piezo resistive pressure sensor. This sensor is created using Sentron’s proprietary full Wheatstone bridge for differential pressure measurements. Thanks to this differential pressure measurement atmospheric changes have no effect. The sensor is stable with low drift in varying pressure and temperature environments.

An OEM pressure sensor module typically consists of sub-assemblies containing the pressure sensor, housing parts and control electronics. The narrow dimensions and the high quality of this pressure sensor make it ideally suited for medical applications in fields such as cardiology, neurology and urology. Examples of applications for which we designed the sensor sub-assemblies are: ventricular pressure-volume measurements for optimization of pacemaker electrode placement, cranial pressure measurement, flow measurement for the world’s smallest heart pump, pressure measurement in urology and gastro-enterology catheters, and in-vivo blood pressure monitoring.

What's next?

By taking a serious look at all applications, we keep entering into new innovations in our semiconductor production facility. Soon we will launch sensors for EC and ORP, with which great multisensor solutions for e.g. water monitoring can be provided. Additionally, we’re looking forward to end the R&D on ion-selective sensors.

For all applications we constantly seek innovations in our semiconductor factory. Soon we will launch sensors for EC and ORP. These can provide great multi-sensor solutions for, e.g., water monitoring. Imagine: all parameters to be monitored using one and the same probe! Additionally, we’re looking forward to finalize the R&D on ion-selective sensors.

The EC is the measure of a material’s ability to allow the transport of an electric charge. This knowledge is important for water-quality monitoring in public water supplies, in hospitals, in boiler water and in industries which depend on water quality such as horticulture and breweries.

Low conductivities are expected for pure water applications like aquaria, household, drinking water and rivers. On the other side, high conductivities are expected for industries like irrigation, greenhouses and manure.

The ORP is the measure of the tendency of aqueous solutions, or any other chemical species, to either acquire electrons from an electrode and be reduced thereby, or to lose electrons to an electrode and be oxidized thereby. This knowledge is important for water-quality monitoring in hydroponics, aquaria, swimming pools, as well as environmental and wastewater sampling. E.g. ORP is an indicator of micro-organism inactivation in a swimming pool or spa pool.

High ORP values (positive potentials) are expected for aerated surface water, rivers, lakes, oceans, rainwater and acid mine water. Low ORP values (negative potentials) are expected in places with limitations in air supply such as submerged soils, swamps and marine sediments.

We started innovative developments on ion-selective sensors that have a membrane mixture suitable for detection of different ions based on the ISFET technology. Selectivity is based on proprietary modifications with several polymer matrix configurations. Nitrate (NO3), Ammonium (NH4+) and Potassium (K+) are currently in development.