What Is This?

FAQ - Explained in a Few Words


Sensor and control engineering uses terms and technologies that are often beyond common knowledge, raising Frequently Asked Questions, FAQ. On this page you can find some basic answers on matters of key importance.

Questions on Ordering

When is my order confirmed?

An order is deemed accepted and confirmed as soon as you have received an order confirmation from us.

Do you grant a discount on larger order volumes or projects?

We review each enquiry to determine whether and to which extent we can grant a discount. This will depend on multiple factors and cannot be generalised.

When will my order be delivered or sent?

Our order confirmations always indicate the calendar week in which the products are dispatched. For example, Shipping date: CW12

How do I proceed if I have a complaint?

For a complaint on one of our products within the warranty period, please send us an email so that we can file the case in a timely manner. You will then receive an ‘REKL-Dxxxxx’ number from our team. With this reference, we ask you to send the product back to our warehouse (Thurn-und-Taxis-Str. 22, 90411 Nuremberg, Germany). See our Warranty Conditions for further details.

How will printing & painting costs be calculated?
Those costs consist of two parts: First, a fixed preproduction or setup rate, and second, the printing/painting costs per unit. A fixed discount, if applicable, will be deducted from the printing/painting costs.
Example: 25 devices shall be painted in RAL 9005 colour.
Preproduction: €167.28 (fixed)
Painting: €16.11 x 25 minus 10 % discount
See page 620 in our Catalogue for individual painting and printing rates.

Questions on Connection & Wiring

What is the difference between a two-wire and a three-wire connection (e.g. on PREMASGARD 21xx and 11xx pressure transducers)?

For a two-wire connection, only two cables (24V and GND) need to be connected to operate the device. A three-wire connection requires the additional connection of the output to ensure that the device will function properly.

If a passive device requires a three-wire connection, which device version do I need?

You will need a version with a four-wire-connection. All S+S sensor devices are available in four-wire versions (if not standard). Where only three wires are needed, the fourth one is simply left open (not connected). The device will still function properly.


What is the difference between absolute and relative humidity?

Ambient humidity is the content of water vapour in air. The capacity of the air to absorb water vapour rises with the temperature. The maximum possible or absolute humidity in warm air or at summer temperatures, therefore, is higher than that in colder air or at winter temperatures. Absolute humidity is indicated in grams of water vapour per cubic metre of air (g/m³). In contrast, relative humidity is the actual percentage of water vapour in air compared to the maximum possible content.

The range of our multifunctional HYGRASGARD products equipped with humidity and temperature sensors can use the measured relative humidity to determine further output variables, such as dewpoint, mixing ratio and enthalpy.

What is the dewpoint?

Ambient air is capable of absorbing more humidity as the ambient temperature rises. The saturation level is indicated in percent, see relative humidity. As the air cools, its relative humidity increases until it eventually reaches its maximum absorption capacity o 100 percent water vapour, i.e. its dewpoint. Further cooling will result in excess water vapour, which is then deposited as dew or condensation.

HYGRASREG Dewpoint Monitors can detect when the dewpoint is being reached. In combination with heating or ventilation devices, this can be used to prevent condensation on the surfaces of chilled ceilings, pipes, etc. Our multifunctional HYGRASGARD devices equipped with humidity and temperature sensors calculate the dewpoint based on the measured relative humidity and ambient temperature.

What is Prodynamic Cross-Convection?

Conventional dewpoint monitors measure the dew formed by condensing humidity on surfaces such as pipes, heat exchangers or concrete ceilings with a humidity sensor positioned in a duct alongside the surface. However, this will not suffice to prevent dew formation. With the S+S patented principle of Prodynamic Cross-Convection, the humidity sensor is exposed to an additional cross-flow of ambient air entering through a transverse hole in the channel. This enables a timely, dynamic detection of imminent dew formation which would occur if the temperature on the surface were to drop below the dewpoint. In this way, a connected controlled blower can be switched on to dry off the condensing humidity.

All HYGRASREG Dewpoint Monitors from S+S work according to the principle of Prodynamic Cross-Convection.

What is the enthalpy of humid air?

The enthalpy of humid air is the heat content of the dry air volume plus the heat content of the water vapour in the air. The enthalpy indicates the possible hat release of a systems and is measured in kJ/kg. In room temperature control, it is considered a parameter of the ‘feel-good climate’.

Our multifunctional HYGRASGARD devices equipped with humidity and temperature sensors use the measured relative humidity and ambient temperature to calculate the enthalpy.

What is the mixing ratio of air?

The mixing ratio is the independent ratio of the mass of water vapour to the mass of water vapour-free air in a volume. It is measured in g/kg and represents an important variable in the control of heating, ventilation, cooling and air conditioning equipment.
Our multifunctional HYGRASGARD devices equipped with humidity and temperature sensors use the measured relative humidity and ambient temperature to calculate the mixing ratio.


Why do passive temperature transducers show deviations?

As non-active measuring elements, passive temperature sensors do not emit a current or voltage signal corresponding to the measured temperature by themselves. Instead, connected controllers can retrieve the elctrical resistance value of the measuring element. However, this value changes not only with the temperature, but also with the resistance of the connection line and contacts. In some sensor types, such as PT100, this can have a significant influence on the measuring accuracy.

In order to compensate the deviations caused by the line and contact resistance, the latter must be subtracted from the measured value either manually or by the controller automatically when using our passive THERMASGARD devices. With our active THERMASGARD measuring transducers, the line compensation is performed internally through the power circuit.


What is differential pressure?

The difference of two pressures is referred to as pressure gradient. Pressure transducers which output this difference as a measured variable or differential pressure must therefore be capable of measuring two different pressures. Differential pressure measuring is used, amongst others, in filter monitoring or volume flow determination.

PREMASGARD pressure transducers from S+S can measure relative and absolute as well as differential pressures. A piezo-resistive measuring elements ensures the highest level of precision.

What is piezo-resistivity, and which advantages does it provide in the sensor technology of pressure transducers?

Piezo-resistive measuring elements make use of the interaction between the electric voltage in a solid body and the mechanical pressure exerted on this solid body, as discovered by the Curie brothers. The term is derived from Ancient Greek ‘piezein’ (to squeeze or compress). The piezo-resistive effect describes the change of the electric resistivity due to pressure and enables very precise pressure measuring.

All PREMASGARD pressure transducers from S+S are equipped with a piezo-resistive measuring element.

Air Quality

What are VOC or mixed gases?

Volatile Organic Compounds (VOC) or mixed gases are characterised by their high tendency to evaporate and affect human well-being and health. Known symptoms span from fatigue and headache to eye irritation and vertigo. In contrast to the CO2 content in room air, most VOC are noticeable by their odour, whereby even those perceived to ‘smell well’ can present a potential health hazard. Typical VOC sources include e.g. flooring and wall cladding, paints and adhesives, furniture and office equipment, but also plants, cleaners and perfumes.

Our AERASGARD air quality sensors determine the VOC content of room air with a measuring element that responds to VOC molecules on its surface while showing only minimal sensitivity for potentially interfering influences, such as temperature and ambient humidity. As a measuring variable of the room climate, the VOC load of the room air is read out in percent. Room ventilation is recommended at values of 60 percent or higher.

What is the purpose o CO2 measuring within buildings?

Carbon dioxide (CO2) is an invisible, odourless gaseous compound of carbon and oxygen, with a content o approx. 0.04 percent (400 ppm) in natural air. CO2 is released both by incineration of carbon containing materials and by exhaling. If the indoor CO2 content is too high, it will impair the well-being an power o concentration of people. The CO2 content is also considered a substitute indicator of potentially virus loaded aerosols in rooms. Therefore, the CO2 value is measured to indicate the need for timely fresh air supply in preventing those risks. The recommended ventilation threshold is 1000 ppm.
AERASGARD Air Quality Transducers for CO2 are equipped with a non-dispersive infrared sensor that uses the light attenuation effect of the CO2 at the wavelength range of 4.26 µm to determine the present CO2 concentration, see NDIR technology.

How does non-dispersive infrared (NDIR) technology work in CO2 measuring?

NDIR sensors for CO2 consist of a measuring system comprising a light source, a measuring distance and a light receiver with a filter. The filter is calibrated to transmit only light in the wavelength range of 4.26 µm, which is typically attenuated by CO2 molecules along the measuring distance. The sensor determines this attenuation and converts it to ppm CO2.

All S+S AERASGARD Air Quality Transducers for CO2 are equipped with a durable NDIR sensor that is automatically recalibrated to the basic value of 400 ppm (normal outdoor CO2 content) at regular intervals. They record the indoor CO2 concentration up to values of 3000 or 5000 ppm.

Why can my CO2 sensor not measure VOC, and why can my VOC sensor not measure CO2?

Since an NDIR sensor for CO2 selectively measures only the light attenuation caused by CO2 molecules, it cannot detect any VOC molecules. CO2 is an inorganic compound. A VOC sensor vice versa responds only to organic mixed gases and thus cannot detect any CO2 molecules.

In most cases, however, CO2 and the VOC content both are critical values for the ‘feel-good climate’ in rooms. Approaches for converting or deriving either of the two values from the other have shown inappropriate and are considered to be misleading. The S+S portfolio of AERASGARD air quality transducers offers several multifunctional devices equipped with an NDIR sensor for CO2 as well as with a VOC sensor.

What is particulate matter?

Dust is divided in standardised particle sizes of coarse, fine an ultra-fine. Fine dust or ‘particulate matter’ (PM) stands for inhalable dust with an aerodynamic particle diameter of less than 10 µm, internationally designated PM10. Respirable fine dust has a size of 2.5 µm or smaller (PM2.5), and any dust particle of 0.1 µm or smaller are categorised as ultra-fine dust.

Fine dust in rooms is caused, amongst others, by oil or wood fired heating, tobacco fumes, asbestos, filterless vacuum cleaners, copier and laser printer toners a well as fungal spores and plants. It can trigger acute and chronic cardiovascular disorders, cancerous diseases and respiratory problems. For outdoors in the European Union, the maximum mean acceptable PM10 value over a period of 24 hours is 50 µg/m³. Indoor values are frequently many times higher than that.

In order to include the PM load in the control of an ideally healthy room climate, several AERASGARD Air Quality Transducers are also equipped with a PM sensor.


When do I need a Modbus or rather an EtherCAT capable measuring transducer?

When do I need a Modbus or rather an EtherCAT capable measuring transducer? Modbus RTU and EtherCAT fieldbuses both enable serial communication between interconnected bus devices. Modbus has emerged as a popular fieldbus system especially in facility engineering, since it builds exclusively on open standards. On the RS485 port, it permits up to 32 participants and transmission speeds of up to 115200 baud. Line distances up to 1000 m are possible at 19200 baud.

EtherCAT is a particularly fast fieldbus system, in which the data packages transmitted over Ethernet (TCP/IP) are no longer received and evaluated or forwarded by each individual participant. Instead, the devices receive only those packages that are meant for them, individually, or add further data in a through-feed process. This enables extremely short cycle times of ≤ 100 µs for realtime applications. Theoretically, up to 65535 participants can b operated on an EtherCAT bus at data rates of 100 Mbaud and higher. In addition, EtherCAT P also reduces the cabling and wiring needs, since it carries data and power over a single joint cable. The system has a proven fit above all in industrial plants.

S+S offers a growing number of multifunctional sensor devices in Modbus and EtherCAT P versions for temperature, humidity, air quality and pressure.

What is the baud rate of fieldbus measuring transducers?
The baud rate (Bd) is the transmission rate of bits per second in data communication. In order to communicate, the baud rate of participants on the fieldbus must be set to the same value. Higher baud rates are often desirable, but more prone to interferences.

On our Modbuscapable devices, the baud rate can be set up to 38400 Bd by means of DIP switches. EtherCAT P capable devices receive their bus parameters from the bus master.
What is the parity in networking with fieldbus measuring transducers?
Parity in data transmission is the EVEN or ODD number of data bits set to 1 in a data byte, including the parity bit. The parity must be identical for all bus participants. In this way, individual bit errors in the transmitted telegrams can easily be recognised.

On our Modbus capable devices, the parity can be set by means of DIP switches. EtherCAT P capable devices receive their bus parameters from the bus master.


What does room climate mean, and is the physical comfort or ‘feel-good climate’’ in rooms measurable?
The room climate depends on several measurable variables, such as temperature and humidity, pollutants (VOC, CO2, particulate matter), lighting (light temperature) and noise, which can be addressed and controlled specifically. However, at which measured values of these variables the individual human being will feel well, can be quite different from person to person and is also a matter of other factors, such as physical activity, actual health, daytime and season.

Controlled ventilation is considered key to a healthy room climate along with sufficient heating, ambient humidity and the lowest possible concentration of pollutants. Multifunctional AERASGARD Air Quality Transducers help building operators master all these parameters and enable a controlled environment adapted to the perceived well-being of occupants. PHOTASGARD Light Intensity and KINASGARD Motion Detectors can complement the ‘feel-good climate’.

Motion and Presence Detectors

How do motion and presence or occupancy detectors work?
In most cases, animals or people who do not move are hard to recognise in the dark, but can be detected with infrared viewing devices since they radiate heat. The primary purpose of motion and presence or occupancy detectors in buildings, however, is the recognition of persons who move, so that e.g. heating and lighting can be controlled depending on room occupancy. Similar considerations apply to the surveillance of protection and security areas, patios and parking lots.

Our KINASGARD Motion Detectors are equipped with a high-sensitivity infrared sensor that will detect even the slightest motion up to a distance of 10 metres.