Generally speaking, we cooperate with our customers via our dealers. If we do not have an agent in your country, there are no obstacles to purchase device directly from one of our departments.

Our technical service support team is at your disposal in order to establish suitable parts for your analyser. After those are determined, the inquiry is channeled to a local dealer, if such is present in your home country.

In our analysers, we install electrochemical cells produced mainly by the companies CityTechnology and Alphasense. Both companies do not possess information about a specific configuration of a madur device and cannot take responsibility for providing inappropriate sensors. Furthermore, the sales policies of both companies exclude the sale of sensors to end-users, and will so always refer to contact the producer of the devices. In order to find out the type of a sensor installed, madur needs the information of the serial number of the device. After the determination, madur communicates the needed information to the local dealer who carries out the sale.

Price lists are prepared for USD. One can choose preferable currency for transactions, as madur accepts payments in both currencies.

We deliver our equipment based on Incoterms 2010 EX-Works terms, which means that the client covers costs of transportation. This enables us to offer our equipment at competitive prices.

Most of our devices, except some exceptions, are manufactured upon specific customer request. Predetermined delivery time, due to this fact, cannot be provided and depends on the configuration and our production capabilities. Installation of non-standard sensor will probably increase the delivery time. Our sales managers designates the delivery time individually for individual order and informs the client using an email. Registered client can track the complete ordering progress on our website.

In technical analysis of gases, by gas concentration we mean volume concentration of this gas component, usually expressed in %, ppm (parts per million) or ppb (parts per billion). Also used symbols: % vol or ppm. Concentration defined this way does not change with changes of gas temperature or pressure, and there is no need to no information about these parameters is needed. Gases to be analysed, in principle, are not dry, and the amount of water contained in them may be subject to a large change (e.g. due to temperature changes). Therefore, the concentration of the gas component in principle mean volume concentration of that component in relation to the dry gas (RH = 0%).

Please use these calculations:

1%	= 10 000ppm
1%	= 10 000 000ppb
1ppm	= 1 000ppb
1%	= 0,000 1%
1ppb	= 0,001ppm
1ppb	= 0,000 000 1%

The mass concentration of the gas expresses the mass of the component in a volume unit of the measured gas. Mass concentration units are mg/l, mg/m³ or g/m³. Mass concentrations are more difficult to work with than volume concentrations as the conditions: temperature and pressure must always be determined.

madur equipment uses STP conditions:

T = 0 °C
P = 1013.25 hPa
RH = 0% (as a default)

There are many other pre-sets used, for example EEA (European Environment Agency) where reference conditions are:

T = 15 °C
P = 1013.25 hPa
RH = 0%

Mass concentration is calculated by multiplying the volume concentration by coefficient distinctive for each gas and its conditions. For a given gas (e.g. CO) many coefficients are available, depending on temperature and pressure. General formula for calculations is:

X [g/m³] = Y [ppm] * M [g/mol] / VA[l/mol]

M – molar mass of a gas
VA – molar volume in STP (standard temperature and pressure) conditions.

During the combustion process both nitrogen oxide (NO) and nitrogen dioxide (NO₂) are created. By simplification, it is usually assumed that the amount of NO is about 95% of all NO_x and the rest is NO₂. In analysers equipped only with NO sensor, the amount of nitrogen oxides is calculated using the formula:

NO_x = NO / 95%

This is approximation method, nevertheless it is commonly used in cheaper analysers.

One of the most common application where gas analysers are being used is hydrocarbons combustion. Besides the CO₂, water is the second large product of the hydrocarbons combustion process, and for this reason the fumes humidity is very high. Due to the high exhaust gas temperature (typically above 100°C), the water remains in the gaseous phase. During the delivery of gas to the analyser, gas sample is cooled down and the water begins to condense. Condensate should be caught by water traps installed in the gas channel, but their effectiveness is usually below 100%. Typically, some of the water condenses in the feed tubes or inside the analyser. Condensate inside the analyser can effectively and for a long period, disrupt the measurements of electrochemical sensors, and in some cases even lead to their malfunction. In case of NDIR analysers inadequate drying and conditioning of the sample will result in a serious damage to the sensors.

Heated hoes is designed to prevent the condensation of water present in fumes. Condensation of water leads to disruption of measurements of gases that dissolve in water (and in some cases makes the measurement impossible). In the gas analysing systems with condensation dryer, condensation should occur in the cooling chamber, so the period of contact of gas sample and water is shortened to the minimum. In gas sampling systems with Nafion® dryer, the gas sample passes through a Nafion® exchanger so condensation does not occur.

The condensation dryer lead the gas sample through a cooling chamber, where temperature is about 0°C. As a result, most of the moisture condenses and is pumped out with peristaltic pump. In modern constructions, the low temperature of cooling chamber is achieved by using Peltier elements.

The advantage of condensation dryer is good value for money (high efficiency / price ratio). The dryer provides sufficient drying of the sample for most of applications. The disadvantage is that there is always water (in liquid phase) present, what results in the loss of gases reacting with water or dissolving in it. In a consequence, it is rather difficult (or sometimes even impossible), and takes a long time to obtain proper measurements (for example of SO₂) with analyser equipped with condensation dryer. Using this type of dryer to test HCl or HF is completely pointless. Necessity of working in a particular position (dryer must “stand on its feet”) is another disadvantage. Nevertheless, due to low price, condensation dryers hold ground of the most popular dryers.

Nafion® is a material manufactured by DuPont, similar to Teflon. Nafion® membrane has ionic properties (permeability of water molecules on the basis of chemical selectivity). In the Nafion® dryer, on one side of the membrane the gas is subjected to drying. On the other side, there is gas that absorbs the filtered moisture. If the condition is ensured that the partial pressure of water in the drying gas is lower than the partial pressure of gas that is used for drying, the excess water will penetrate from the gas sample to the drying gas until the partial pressure is equal on both sides of the membrane. This process also occurs when the water is in gaseous phase and is very fast – about one second is enough for the pressure to level and stabilise.

The main advantage of this dryer is its high selectivity – only water is being removed, without the loss of any other components (attention: there are exceptions!). Water is removed very quickly, already from the gaseous phase. Since there is no water condensation, there is no effect of loosing of gases soluble in water. Nafion® dryers are ideal for the measurement of gases such as HCl, Cl₂, HF and SO₂. The advantage is the simplicity of design and the ability to work in any position. The main drawback is their higher price (in comparison to condensation dryers) due to the high cost of Nafion® membrane itself. Another disadvantage is the gradual loss of efficiency during the life of Nafion® membrane. These dryers cannot be used for measurements of certain compounds such as alcohols and ammonia (NH₃).

Every electrochemical sensor under the extended influence of measured gas deteriorates. Measurements, particularly of the low concentrations, are then burdened with a higher error. Periodic ventilation allows the sensor to recover its full accuracy. If the concentration of provided gas is high then the ventilation should be performed more frequently. During ventilation process all of the toxic gas sensors are assigning their gaseous zeros and the O2 sensor designates its measuring range (calibrates itself on the atmospheric air).

Over many years of production, we have observed that the parameters of electrochemical sensors change most rapidly at a rather initial stage of their use. In order to widely avoid this event, during production of the devices, we apply a method to stabilise the parameters of the sensors. This is what we name forming of the sensors, which generally bases on reviving them periodically through administration of concrete doses of certain gases. A sensor that underwent this process of forming before the first calibration is effectively more stable over time and this way ensures the durability of the calibration impact.

A common disadvantage of practically all electrochemical sensors is their limited selectivity. This means that the sensor does not react only to the gas it should detect (e.g. H₂S), but also to other components being part of the measured gas (e.g. SO₂). In practise, this means that sensor H₂S will give an electrical signal just because of the presence of SO₂, even in case of total absence of H₂S. Cross-sensitivity concerns all electrochemical gases and can be accumulative (the foreign gas increases the signal of the sensor) or diminutive (the foreign gas decreases the signal of the sensor).

The leading producers of sensors are attempted to construct them in a way that they obtain the lowest possible sensitivity towards foreign gases. In practise, this helps to reduce, but not avoid the effect of cross-sensitivity. Another method is to equip the sensors with built-in filters that eliminate the foreign gases. The main disadvantage is the limited durability of the filters and in further consequence lower effectiveness of this method. The most sophisticated method used by advanced producers of gas analysers is the calculated elimination of the cross-sensitivity.

We use all available methods: a. we use solely high-quality sensors with minimised cross-sensitivity from the leading producers, b. we use sensors that are equipped with filters for foreign gases, c. our analysers are calibrated with many single-component gases and the cross-sensitivity is eliminated during measurements by calculation.

Suppose the analyser is equipped, besides sensor O₂, with 5 more following electrochemical gas sensors: CO, NO, SO₂, NO₂ and H₂S. In this case, sensor H₂S will react sensitive not only to his own component, but also the remaining gases. This reaction pattern applies to other sensors as well. During the process of calibration the analyser with its sensors is being fed with corresponding single-component gases. The reaction of each sensor to each gas is then noted and saved in the long-term memory of the analyser in a form of a two-dimensional calibration table. During the measurements, the analyser uses the calibration table and electrical signals from all electrochemical cells to solve the series of equations to calculate the results for all sensors, that are deprived of cross-sensitivity error.

Calibration with gas mixtures is used to facilitate the process of calibration, mainly in terms of saving time of the calibration process. This, however, implies that there is no cross-sensitivity between the sensors, which is not really true. Even if instantly after production of a device, thanks to new filters in the sensors, the cross-sensitivity is almost zero, this value will get worse with increasing operating life of the filters implemented. In such a situation, a gas mixture calibrated device will measure the gas mixture in a correct way, but will show faulty results in case of other proportions of gases to be measured. Thanks to our calibration method and calculated elimination of cross-sensitivity, our devices will show correct results even with exhausted filters. In our practice, we also use gas mixtures, but only to control the operation of the devices and never for calibration purposes.

Yes. Despite the efforts of producers, all electrochemical sensors show a significant and mostly non-linear dependency of the signal on the temperature. All madur analysers have a built-in thermal compensation of the sensors, basing on a non-linear algorithm and constant temperature measurement of the sensors with an accuracy of 0.1°C (sometimes even 0.01°C). However, this method is not always sufficient, as the thermal characteristics of sensors change during their life-times and the compensation becomes less efficient over time. In most advance solutions we also use active thermal stabilisation that allows us to stay almost completely free the from the influence of temperature.

Producers, that use these kinds of sensors emphasise the simplicity of replacement and absence of calibration necessity. On the other hand, due to the built-in electronics, the price of such a sensor rises significantly. Moreover, it is not true that such a sophisticated sensor does not need any calibration anymore, because it lasts for only six months, whereas the life-time of the sensor itself may be rather longer. So, in order to receive correct measurement results, the user would have to buy a new pre-calibrated sensor every six months, which constitutes a quite cost-intensive issue. Therefore, we have rather quickly discarded the idea of using such sensors, especially as our clients appreciate the independence in the purchase of sensors. The algorithms for calibration are accessible in all our analysers, so that the user can perform calibration by oneself or any other facility that offers such service. Using pre-calibrated sensors, in our opinion, resembles the politics of manufacturers of ink-jet printers. Users of these printers will definitely know what we mean.

Electrochemical sensors are based on electrolyte that wears out slowly while the sensor is being used. The expected operating lifetime of sensor is determined by concentration of a gas sample and the time that the sensor is exposed to it.

Classic electrochemical sensor measures concentration of a gas, independently from air pressure (if air pressure changes measurement stays the same). Sensor that measures partial pressure works in a different way. It measures the hypothetical pressure of that gas if it alone occupied the volume of the mixture at the same temperature. So if air is measured in 1000hPa pressure, oxygen partial pressure sensor should measure about 209,5ppm of oxygen (as amount of oxygen in atmosphere equals 20,95%). Measurement can change either because the concentration changes or because the pressure does.

BIO-gas consist mainly of methane and carbon dioxide, complemented with trace concentrations of other gases like Hydrogen sulfide. Gas analyser for BIO-gas applications should be equipped with CO₂ and CH₄ sensors (optionally with H₂S and O₂). madur supplies NDIR sensors for CH₄ and CO₂ and our analysers are suitable to measure BIO-gas. Based on years of our experience with calibration of gas sensors, we have noticed that signal of CH₄ sensor slightly depends on how it is calibrated (CH₄ in balance of N₂ or CH₄ in balance of CO₂). By and large, factory calibrations are made with reference gas in balance of nitrogen. If the analyser designed for BIO-gas application is equipped with both CO₂ and CH₄ sensors, the concentrations of both compounds are known. Then the analyser can compensate the effect of the above mentioned phenomenon. Sometimes the analyser is equipped with just the CH₄ sensor – in this situation, to achieve the optimal effect of the BIO compound measurement, the calibration of CH₄ sensor must be performed with CH₄ gas in balance of CO₂. If the analyser is equipped with CO₂ sensor, this must be calibrated with gas CO₂ in balance of CH₄.

Please ask every unusual questions to our sales department. Sales technician will answer it directly or consult it, if it is necessary, with our R&D department. If the question is sophisticated then R&D department engineer will contact you directly.

Yes, firmware modification or upgrade is possible on a paid conditions. Contact our sales department to determine details. In some cases, it is advised to upgrade the firmware as it may contain fixes to errors and/or new functions. In most of our devices, firmware upgrade is easy to perform and available to the client.

Our standard offer delivers sensors (NDIR and electrochemical) for the most common combustion gases and measuring ranges. Most of the modifications concerns changes of the sensors' measuring ranges and incorporation of sensor measuring less popular gases. We can also adapt our analyzer's gas connectors to the client's installation system. Firmware and software modification to the client's needs like data collection standard or communication protocols is also possible.

We follow the rule that if the customised modification does not exceed the usual costs of the production of a comparable device, and furthermore has a potential to be integrated as a new option in our devices, we do not charge any additional costs. Only the delivery date may be exceeded in such cases.