Convert RTD Reading VI

Owning Palette: Scaling VIs

Requires: Base Development System

Converts a voltage you read from an RTD into temperature in Celsius. Wire data to the RTDvolts input to determine the polymorphic instance to use or manually select the instance.

Details  

Use the pull-down menu to select an instance of this VI.

Select an instance Convert RTD Reading (waveform)Convert RTD Reading (scalar)

Add to the block diagram

Find on the palette

Convert RTD Reading (waveform)

	Ro is the RTD resistance at 0° C. The default is 100 Ω.
	RTDvolts is the voltage you read from the RTD.
	Iex is the excitation current you used with the RTD. This parameter defaults to an excitation current of 0.15 mA.
	A is a coefficient of the Callendar Van-Dusen equation that fits your RTD. The default coefficients are those for the European curve (also called the DIN 43760 standard).
	B is a coefficient of the Callendar Van-Dusen equation that fits your RTD. The default coefficients of this equation are those for the European curve (also called the DIN 43760 standard).
	RTDtemp is the return temperature value in degrees Celsius.

Convert RTD Reading (scalar)

	Ro is the RTD resistance at 0° C. The default is 100 Ω.
	RTDvolts is the voltage you read from the RTD.
	Iex is the excitation current you used with the RTD. This parameter defaults to an excitation current of 0.15 mA.
	A is a coefficient of the Callendar Van-Dusen equation that fits your RTD. The default coefficients are those for the European curve (also called the DIN 43760 standard).
	B is a coefficient of the Callendar Van-Dusen equation that fits your RTD. The default coefficients of this equation are those for the European curve (also called the DIN 43760 standard).
	RTDtemp is the return temperature value in degrees Celsius.

Convert RTD Reading Details

This VI first finds the RTD resistance by dividing RTDVolts by Iex. The VI then converts the resistance to temperature using the following solution to the Callendar Van-Dusen equation for RTDs.

Rt = Ro[1 At Bt² C(t–100)t³]

For temperatures above 0° C, the C coefficient is 0, and the preceding equation reduces to a quadratic equation for which the algorithm implemented in the VI gives the appropriate root. So, this conversion VI is accurate only for temperatures above 0° C.

Your RTD documentation should give you Ro and the A and B coefficients for the Callendar Van-Dusen equation. The most common RTDs are 100, 500, or 1000 Ω platinum RTDs that follow either the European temperature curve (DIN 43760) or the American curve.

The following table gives the values for A and B for the European and American curves.

European Curve (DIN 43760)	American Curve
A = 3.90802e–03	A = 3.9784e–03
B = –5.80195e–07	B = –5.8408e–07
(= 0.00385; = 1.492)	(= 0.00392; = 1.492)

Some RTD documentation gives values for and , from which you can calculate A and B using the following equations.

A	= (1 /100)
B	= – /1002