Sensors for Temperature and Humidity With 1-Wire® Bus Interface
The 1-Wire bus is a serial interface produced by Analog Devices, which enables measured values to be transmitted between a master (controller) and one or more temperature sensors via a common data line. The special thing about this bus is that both the power and the data are transmitted via a single line.
Truth be told, you can’t actually transmit the signal with just a single line. You also always need at least one ground connection (GND). This means you need one line for the signal and power supply (DQ/VDD) and one line for the ground connection (GND).
In what is known as “parasitic” mode, the temperature sensor is supplied with operating voltage via the data line (DQ). As an alternative, you can also operate in 3-wire mode, in which case the operating voltage and the data line are separated from one another. One advantage of this mode is lower susceptibility to interference, which permits longer line lengths.
A 1-Wire bus network consists of a master (controller) and up to 100 temperature sensors. Line lengths of up to 100 m are possible in parasitic mode, and up to 300 m in 3-wire mode. The temperature sensors are identified and addressed via a unique serial number that is pre-programmed at the factory and cannot be changed.
Temperature sensor with integrated 1-Wire bus interface
A temperature sensor with an integrated 1-Wire bus interface offers a number of advantages over a classic temperature sensor:
- Thanks to the bus topology, all sensors are connected to a single line, which results in significantly less cabling and space requirements.
- Assignment is simple, since each temperature sensor is supplied with a unique serial number. For easier identification of the temperature sensors, SIKA prints the serial number in plain text on the sensor.
- Because the measured values are transmitted digitally, there are no errors due to long line lengths or interference.
- Integration is comparatively simple and cost-effective since, in most cases, no further hardware is required apart from the 1-Wire bus master.
SIKA temperature sensors with an integrated 1-Wire bus interface include the WGF and WBA types, which are used to great effect in rail vehicles for measuring the air temperature in ventilation ducts and the surface temperature of floor heating elements, among other applications.
Multisensor for temperature and humidity
One particularly intriguing application is to combine multiple measurement parameters. The WHS multisensor from SIKA offers a combined temperature and humidity sensor with a 1-Wire interface, which measures the relative humidity in addition to the temperature and transmits both digitally. This not only reduces the amount of cabling but also eliminates the need for an additional measuring point, which offers both technical and cost advantages.
Added protection and reliability
The SIKA 1-Wire bus products always include an additional protective circuit to guard against electromagnetic interference and voltage peaks. This protective circuit enables interference-free operation even under the influence of interference fields or in the case of line interference caused by other electrical/electronic devices.
The temperature sensors have been type-tested in accordance with DIN EN 50155 to ensure reliable operation under extreme environmental influences. This standard defines the requirements for electrical equipment in rail vehicles and includes test specifications for the power supply, EMC, temperature, humidity, shock and vibration resistance.
The WGF and WBA temperature sensors also feature a process connection made from glass fibre reinforced plastic, which has very good insulation properties. This significantly reduces the heat dissipated via the temperature sensor and minimises the heat dissipation error.
