Fuji Electric FRENIC-HVAC User Manual page 462

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
function code H27.
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.
PTC
thermistor
When using the terminal [C1] for PTC thermistor input, also turn SW5 on the
control printed circuit board to the PTC side. For details, refer to Chapter 2,
"SPECIFICATIONS."
is calculated by the expression below. Set the result V
v2
R
p
10.5
= ×
V
V2
27000 + Rp
[13]
DC +10 V
Resistor
27kΩ
(Operation level)
SW5
[C1]
H27
C1
PTC
[11]
6-152
(V)
<Control circuit>
Comparator
External
alarm
H26
0 V
to
v2