Fluke 2640A, 2645A user manual Using the Custom-385 RTD with Other Platinum RTDs, Error Degrees C

RTD Linearization

Custom-385 RTD D

Using the Custom-385 RTD with Other Platinum RTDs D-4.

Although the Custom-385 RTD linearization uses a β and δ from a 385 RTD, other RTD types can be used. The Custom-385 linearization will compensate for the change in α, but errors will be introduced due to the difference in the δ and β coefficients of the RTD and the fixed coefficients. Figure D-2 shows the accuracy envelope for a 375 RTD. Because of the error introduced by the approximation and the difference in δ it is recommended that the use of the 375 RTD be limited to temperatures between -100°C and 300°C. Figure D-3 shows the accuracy envelope for a 391 RTD and Figure D-4 shows the accuracy envelope for a 392 RTD. Due to errors introduced by the approximation and the difference in δ it is recommended that the use of the 391 RTD and 392 RTD be limited to temperatures between -100°C and 600°C.

Accuracy Envelope: Custom RTD, 375 Probe

1 Year Slow: 18-28 Degrees C

Alpha: 0.00375 Delta: 1.605 Beta: 0.16

Error - Degrees C

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

2645A 2640A

-100 -50 0 50 100 150 200 250 300

Temperature - Degrees C

Figure D-2. 375 RTD

D-3