Rockwell Automation 1397 Pulse Encoder Interface Installation Inst. - Manual (Page 3)

1397 Pulse Encoder Interface Card 3
1397-5.13 June, 1997
One pulse/scan is required to meet the specified drive speed regulation
listed in the 1397 User Manual. For a drive scan time of 0.02 seconds,
the card requires a minimum of (50) pulses-per-second from a pulse
encoder. Using a minimum motor speed of 25 RPM:
PPR
1
= [1]
×
[60] = 120 PPR
——————
25
×
[0.02]
Step 2 — Determine the maximum allowable pulse encoder PPR.
To leave adequate "head room" for possible motor over speeding at
the motor’s rated nameplate speed, the card’s "head room" frequency
should not exceed 73kHz, the card’s maximum frequency.
where:
PPR
2
= The Maximum Allowable Pulse Encoder
PPR
N
2
= P.041 [Max Motor Speed]
PPR
2
= 73,000
×
60 Sec/Min
———————————
N
2
PPR
1
≤
PPR
req
≤
PPR
2
where PPR
req
= The PPR Required for the Application
Step 3 — Pick a PPR for the application.
Pick a PPR for the application between the values calculated in Steps
1
& 2.
Step 4 — Calculate the pulse encoder’s required frequency at P.041
[Max Motor Speed].
Using the value selected in Step 3, calculate the pulse encoder
frequency at P.041 [Max Motor Speed].
where:
Freq
req
= The Pulse Encoder’s Required Frequency
PPR
req
= The PPR Required for the Application
Freq
req
= N
2
×
PPR
req
———————
60
Freq
req
≤
80%
×
Freq
PE
where Freq
PE
= The Pulse Encoder’s Maximum Rated Nameplate Frequency.
Step 5 — Confirm that the pulse encoder frequency
≤
80% of the pulse
encoder’s maximum rated nameplate frequency.
To ensure that the pulse encoder has adequate "head room" for motor
overspeeding, confirm that the pulse encoder’s required frequency is
≤
80% of the pulse encoder’s maximum rated nameplate frequency.
How to Select the PPR of
a Pulse Encoder
(continued)