Fuji Electric FRENIC-Ace series - Page 335

5.3 Description of Function Codes
5-165
FUNCTION CODES
Chap 5
■ Thermistor (for motor) (level) (H27)
H27 specifies the detection level (expressed in voltage) for the temperature sensed by the PTC thermistor.
• Data setting range: 0.00 to 5.00 (V)
The alarm temperature at which the overheat protection becomes activated depends on the characteristics of the
PTC thermistor. The internal resistance of the thermistor will significantly change at the alarm temperature. The
detection level (voltage) is specified based on the change of the internal resistance.
Suppose that the internal resistance of the PTC thermistor at the alarm temperature is Rp, the detection level
(voltage) V
v2
is calculated by the expression below. Set the value of V
v2
to function code H27.
)V(5.10
R51000
R
V
p
p
2V
×
×+
=
Connect the PTC thermistor as shown below. The voltage obtained by dividing the input voltage on terminal [C1]
with a set of internal resistors is compared with the detection level voltage specified by H27.
When using the terminal [C1] for PTC thermistor input, also set SW4 on the control printed circuit board
to the PTC side. For details, refer to
Chapter 2, Section 2.2.8.
PTC thermistor
internal resistance
Alarm temperature
Temperature
PTC
thermistor
Thermistor detection
level
Comparator
Mode
selection
“THM”