Phason
VTC-1D user manual
11140010
7
The difference in motor power factors can cause the actual differential to be less
than the displayed value. If the power factor of the motor is available, use the
correction numbers and formula below to calculate the correct differential setting.
Power factor
1.0 0.9 0.8 0.7 0.6 0.5
Correction (
°
F)
1.00 1.05 1.10 1.25 1.33 1.60
actual differential = desired differential
×
correction
Example 1
To have an actual differential of 6°F with a motor that has a power factor of 0.7, set the differential to
7.5°F.
6°F
×
1.25 = 7.5°F
Example 2
To have an actual differential of 5°F with a motor that has a power factor of 0.5, set the differential to
8.0°F.
5°F
×
1.6 = 8.0°F
If you do not know the power factor, calculate the correction as follows:
1.
Set the idle speed properly. For more information, see
Setting minimum ventilation in idle mode
on
page 8.
2.
Set the differential to 10°F with the internal trimmer. Note the temperature (
T1
) in the digital display.
3.
Press and hold the switch to the right and adjust the temperature set point to equal the temperature from
step 2. The fan operates just above the idle speed.
4.
Slowly decrease the temperature set point and listen to the fan increase in speed. When the motor reaches
full speed, note the temperature set point (
T2
).
5.
Calculate the correction using the following formula.
Correction = 10°F ÷ (
T2
–
T1
)
Example 3
For a T1 temperature of 75°F and a T2 temperature of 82°F, the correction is 1.43.
10°F ÷ (82°F-75°F) = 1.43
If the desired differential is 5°F, the actual differential can be calculated as follows: 5°F
×
1.43 =
7.15°F.
Set the differential to 7°F for an actual differential of 5°F.
