Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 152)

152 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 2 Feedback and I/O
PTC Motor Thermistor Input A PTC (Positive Temperature Coefficient) sensing device, also known as a motor
thermistor, embedded in the motor windings can be monitored by the drive for
motor thermal protection. The motor windings are typically equipped with three
PTC sensors (one per phase) wired in series as shown in schematic below. The
miniaturized sensors have a low resistance below the rated response temperature,
and increase their resistance (exponentially) in the rated response temperatures
range. The rated response temperature is defined by the PTC sensor. Motors with
different thermal insulation classes (Class F or H) are equipped with different
PTC sensors, each with its own response temperature such as 120, 130, and 140
Degrees C. Unlike the PT100 or KTY thermistors, which have a linear relation
between temperature and resistance, the PTC thermistor is used for a
temperature level indication rather than a direct measurement in degrees C.
Figure 13 - PTC characteristic temperature/resistance curve according to IEC-34-11-2
Hardware and Connection
The PTC thermistor leads are connected to the PTC+ and PTC- terminals of
either the PowerFlex 753 main control board TB1 or to TB1 of one of the
optional I/O cards, catalog numbers 20-750-2262C-2R, 20-750-2263C-1R2T,
20-750-2262D-2R.
PTC thermistors of ATEX certified motors connect to the ATEX option
module, 20-750-ATEX, which is mounted onto one of the 11-Series I/O cards,
catalog numbers 20-750-1132C-2R, 20-750-1133C-1R2T, 20-750-1132D-2R.
4,000
1,330
550
250
100
TNF – 20K
TNF – 5K
TNF + 15K
TNF + 5K
20
10
-20 ˚C
0 ˚C
TNF
R[Ω]
R
TNF
ϑ
Resistance in sensor circuit in ohms
Temperature
Rated response temperature tolerance
limit in degrees C
Defined cutoff values