# Mitsubishi Electric FR-A820-00046 Instruction Manual Page 416

(F) Setting of acceleration/deceleration time and acceleration/deceleration pattern
Deceleration time setting (Pr. 8, Pr. 20)
● Use Pr. 8 "Deceleration time" to set the deceleration time required to reach a stop status from to
Pr. 20 "Acceleration/deceleration reference frequency".
● Set the deceleration time according to the following formula.
Deceleration time setting
Example
For example, the following calculation is used to find the setting value for Pr. 8 when increasing the
output frequency to the maximum frequency of 50 Hz in 10 s with Pr. 20 = 120 Hz and Pr. 10 = 3 Hz.
Pr. 8 = 120 Hz × 10 s / (50 Hz - 3 Hz)
≈ 25.5 s
NOTES
If the acceleration/deceleration time is set, the actual motor acceleration/deceleration time can-
not be made shorter than the shortest acceleration/deceleration time determined by the mechan-
ical system J (moment of inertia) and motor torque.
If the Pr. 20 setting is changed, the Pr. 125 and Pr. 126 (frequency setting signal gain frequency)
settings do not change. Set Pr. 125 and Pr. 126 to adjust the gains.
Under PM sensorless vector control, if the protective function (E.OLT) is activated due to insuffi-
cient torque in the low-speed range, set longer acceleration/deceleration times only in the low-
speed range in Pr. 791 "Acceleration time in low-speed range" and Pr. 792 "Deceleration time in
low-speed range".
Changing the minimum increment of the acceleration/deceleration time (Pr. 21)
● Use Pr. 21 to set the minimum increment of the acceleration/deceleration time.
– Setting value "0" (initial value): minimum increments 0.1 s
– Setting value "1": minimum increments 0.01 s
Pr.21 setting allows the minimum increment of the following parameters to be changed:
Pr. 7, Pr. 8, Pr. 16, Pr. 44, Pr. 45, Pr. 110, Pr. 111, Pr. 264, Pr. 265, Pr. 791, Pr. 792
NOTES
Pr.21 setting does not affect the minimum increment setting of Pr. 611 "Acceleration time at a
restart".
The parameter can be set in five digits including the numbers below decimal point for the
FR-DU08 and the FR-PU07. A "1000" or more value is set in increments of 0.1 s even if Pr. 21 = "1".
5 - 236
Pr. 20
Deceleration time from maximum frequency to stop
×
=
(Maximum frequency – Pr. 10)
Parameters