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Multi Zone Temperature Reading

Today I am going to introduce a number of products we have recently added to our line up that allow you to read the temperature in multiple areas from the one device and explain suitable applications and the advantages of each.

We have two main groups to look at, a group that reads thermocouples and a group that reads semiconductor temperature sensors like the DS18S20 and DS18B20.

Thermocouple compatible devices

Thermocouples are temperature sensors which are made of two different types of metal which create a known voltage for a given temperature. Since thermocouples are basic in design, just consisting of two wires joined at the sensing point, thermocouple probes are easily made for wide temperature ranges ranging from -270°C to +1700°C easily covering all but the most extreme temperature measurement requirements. However, thermocouples are generally not as accurate as semiconductor devices.

Some applications where Thermocouples are advantageous over other types of temperature sensors:

  • Automotive – Engine, Exhaust and Brake temperatures are higher than most temperature sensors can handle, but within the range of Thermocouples.
  • Ovens, Furnaces and Kilns – At temperatures where other temperature sensors will not operate.
  • Freezer or Cryogenic monitoring – Where temperatures are well below 0°C.
  • Chemical Processes – Where corrosive chemicals may damage probes or reach high temperatures thermocouples are more readily available for such processes.
  • Multi-Zone Temperature Monitoring, Data Acquisition or Logging Systems– With cheap readily available thermocouples.

In this group we have:

  • The KTA-259v3 Thermocouple multiplexer shield
  • The KTA-260 Labjack thermocouple multiplexer

KTA-259V3 connected to Arduino Controller and 2 K-Type Thermocouples

First up we have the KTA-259v3 Thermocouple multiplexer shield, it is designed to connect up to 8 thermocouples of the same type (K, J, N, S, T, E or R) to an Arduino controller, an example Arduino sketch shows how to read each channel and can be modified to suit any protocol that is desired. A different model is available for each of the listed thermocouple types. An older version of the KTA-259 is available while stocks last at a reduced price, it is based on a different thermocouple to digital conversion IC which is limited to K-Type thermocouples in the range 0-1024°C but comes with Arduino stackable headers installed, whereas for the new version the headers are sold separately.

KTA-260 connected to LabJack U3-LV and 2 K-Type Thermocouples

Next we have the KTA-260 Labjack thermocouple multiplexer, it is based on the same circuit as the KTA-259v3 but is designed like an LJTick Module for the LabJack UD Series of data acquisition units. An example DAQFactory project shows how to use the KTA-260 and can be used to immediately read the temperatures and display or log them on a PC. DAQFactory express is free and comes with each LabJack unit, though to use all the features you need to upgrade.

Semiconductor compatible devices

Semiconductor type temperature sensors can have a greater accuracy and resolution than thermocouple temperature sensors but the range of temperatures for which they are suitable is limited. The DS18S20 and DS18B20 temperature sensors that work with this range of devices are limited to -55°C to +125°C.

In this group we have:

  • The KTA-279 5 Channel Modbus Temperature Sensor
  • The KTL-279 5 Channel Modbus Temperature Sensor with LCD
  • The KTA-280 Arduino Based 5 Channel Temperature Sensor
  • The KTL-280 Arduino Based 5 Channel Temperature Sensor with LCD

KTA-279 (Left) and KTL-279 (Right)

The KTA-279 and KTL-279 take up to 5 DS18S20 or DS18B20 temperature sensors and hold the readings in Modbus Holding Registers. Modbus is an industrial communications protocol, usually transmitted over RS485 and most SCADA systems will be able to easily communicate with Modbus. Additional to the RS485 port for communication is a USB port for easy connection to a PC and the KTL version includes a 8x2 character LCD for displaying the temperature readings locally.
The KTA-280 and KTL-280 use the same hardware as the "279" variants but the "280" variants do not use the Modbus Protocol, they simply transmit ASCII data out the USB and RS485 ports and this can be monitored with any terminal emulator program (RealTerm is a great, free, terminal emulator).
The KTA-280 and KTL-280 variants can be user reprogrammed using the Arduino Environment as the hardware ships with the Arduino Bootloader installed and the source code for them is available on the KTA-280 product page. This is great if you want to make the device communicate with some existing piece of equipment or software or to modify the firmware to add more features.

The GJS-001 Waterproof DS18S20 Probe can plug directly in to the devices and the KTA-001 Wall Mount DS18S20 Temperature Sensor can be plugged in using a 6P6C extension cable.
In addition to temperature sensors, the "279" and "280" devices can be used to monitor Wind Speed and Wind Direction using the ANM-001 Anemometer and Solar Radiation can be monitored using the ANM-003 Solar Radiation Sensor.
The combination of Incoming Water Temperature, Outgoing Water Temperature and Solar Radiation can be used to calculate the efficiency of Solar Hot Water Collectors, great for those trying to get the most out of their system.

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