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Using a 3-Wire RTD to Prevent Temperature Measurement Errors

Ensure High Accuracy in Your Critical Temperature Measurements

To prevent inaccurate temperature measurements which can potentially cause disastrous inventory losses, CAS DataLoggers recommends using 3-wire RTDs to customers taking temperature measurements using RTD sensors. These sensors are affordable and easily available for use with our wide inventory of temperature dataloggers, but some users are unaware of this more accurate option. With this in mind, Applications Specialists have put together this brief guide to show the need for 3-wire RTDs.

RTD sensors make simple resistance measurements, usually at about 100 ohms, which is a relatively low level of resistance. Therefore an RTD measurement error of 1 ohm or more is quite significant– for a regular RTD at room temperature, the resistance is 109.1 ohms, and even a 1-ohm error in that measurement will cause a temperature error of about 2.5°C. When using a 2-wire RTD, users may find that the resistance of the connections between the sensor and datalogger directly affects the temperature measurement, so this is easily avoided by using a 3-wire RTD, which enables the connected datalogger to compensate for the resistance of the circuit.

An example of this kind of measurement error occurs when connecting an RTD to a piece of 20-gauge hookup wire, with the resistance at about 1 ohm per 100 ft. of cabling. In this case, using a 2-wire RTD with a 50-ft cable on it can result in a 2° to 2.5°C temperature error due to the resistance of the wire. So especially with longer cable runs, users can avoid this significant inaccuracy by using a 3-wire RTD sensor along with a data logger that provides automatic compensation for these types of applications.

CAS DataLoggers products are used in a wide variety of applications in remote monitoring, in industrial process and manufacturing industries, for automotive and aerospace data collection, in pharmaceutical manufacturing and storage, and in geological and environmental monitoring—there are even units on the Space Shuttle and ISS (International Space Station)!

Sophisticated data acquisition and control systems are also available including high performance real-time systems for situations where traditional test systems or programmable controllers are not suitable. These systems are used in data acquisition, test and control applications where microsecond precision is needed. Models are available with 8 to over 400 analog input channels, analog output channels, digital inputs and outputs, counters, RS-232, RS-485 CANbus and Profibus interfaces. CAS DataLoggers also provides configuration assistance, custom programming, custom system design and assembly, post-sales technical support, and repair and calibration services. Development capabilities include custom data acquisition and data logging systems, test and measurement systems, and portable data collection systems.