allen-bradley bulletin 1336 plus encoder feedback & pulse train input

ALLEN-BRADLEY
ALLEN-BRADLEY
BULLETIN 1336 PLUS
ENCODER FEEDBACK &
PULSE TRAIN INPUT
APPLICATION NOTE # 1336S - 21
June 24, 1997
PURPOSE
The purpose of this document is to provide guidelines for wiring and control
schemes for the Bulletin 1336 PLUS AC Drive. This document is to be used as a
suggestion only. Users must ensure that installations meet applicable codes and
are suitable for the existing conditions.
WHAT THIS NOTE
CONTAINS
The 1336 PLUS drive can be configured with an encoder feedback card that
allows closed-loop control of induction motors. This feature allows the motor to
react quickly to changes in the load to maintain the desired RPM. The drive
hardware and parameter set up will be examined to allow simple integration of
this feature.
INTENDED
AUDIENCE
This application note is intended to be used by personnel familiar with the
hardware components and programming procedures necessary to operate the
Bulletin 1336 PLUS.
WHERE IT
IS USED
The diagrams, parameter settings, and auxiliary hardware used in this application
note are designed to address specific issues in many different applications. Some
changes by the Users may be necessary to apply the concepts of this document
to a specific application.
TERMS AND
DEFINITIONS
GROUP
Categorized block of parameters with related functions.
ELEMENT
Individual parameters within a group.
[]
Denotes a parameter name.
L4E
TTL interface board with encoder inputs.
L5E
24Vdc interface board with encoder inputs.
L6E
115Vac interface board with encoder inputs.
NOTE: The Encoder Feedback and Pulse Train Reference inputs are mutually
exclusive. Refer to Pulse Train description for further information.
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ALLEN-BRADLEY
DESCRIPTION
ENCODER FEEDBACK
Encoder Feedback control of the 1336 PLUS drive performs closed-loop velocity
regulation. The response characteristic is defined in terms of recovery time. This
type of control strategy allows the simplest integration of velocity regulation by
allowing the User to manipulate a single parameter to achieve the desired
response. Refer to Figure #1 for software diagram.
LOAD
LIMITER
LIMITED
INVERTER
SECTION
FREQUENCY
REFERENCE
ROTOR
SPEED
HOLD
INTEGRAL
GAIN
VELOCITY
FEEDBACK
Figure 1
To program the 1336 PLUS for Encoder Feedback the [Speed Control]
parameter, located in the FEATURE SELECT group, must be set to "Encoder
Fdbk". Next, the ENCODER FEEDBACK group must be set up. [Encoder Type] is
used to select either a "pulse" or "quadrature" type encoder. The value
programmed in [Pulse/Enc Scale] is the nameplate PPR of the encoder.
[Maximum Speed] sets the upper limit for the encoder feedback operation. To
operate above this setting, program [Maximum Freq] to a value greater than
[Maximum Speed]. The integral gain is adjusted with parameter [Speed Ki]. The
nameplate rpm of the motor is entered into [Motor NP RPM]. The nameplate
rated frequency is set in parameter [Motor NP Hertz]. An example of parameter
settings is shown in Table #1.
Table #1
NUMBER
GROUP
NAME
SETTING
77
Feature Select
Speed Control
Encoder Fdbk
152
Encoder Feedback
Encoder Type
Pulse
46
Encoder Feedback
Pulse/Enc Scale
1024
151
Encoder Feedback
Maximum Speed
60
165
Encoder Feedback
Speed Ki
2000
177
Encoder Feedback
Motor NP RPM
1750
178
Encoder Feedback
Motor NP Hertz
60
Other parameters, located in the ENCODER FEEDBACK group are "read only"
type. Those parameters are shown in Table #2.
GROUP
PARAMETER
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Table #2
TYPICAL VALUE
ALLEN-BRADLEY
Encoder Feedback
Encoder Feedback
Encoder Feedback
Encoder Feedback
Encoder Feedback
Motor Poles
Speed Error
Speed Integral
Speed Adder
Pulse/Enc Hertz
4
0.0 - +1.0
0.0 - +1.0
0.0 - +1.0
operating frequency
Required Hardware - For interconnection of the encoder signals to the drive, one
of the control interface boards (L4E,L5E or L6E), with the encoder inputs, is
necessary. The control interface board has two jumpers, JP3 & JP4, that must be
set to the voltage level of the encoder output. When utilizing the drive (internal)
power source with JP3 & JP4 set for 12 volts, the minimum on voltage is 7Vdc.
When JP3 & JP4 are set for 5 volts, the minimum on voltage is 3Vdc. With an
external power source, the minimum on voltage is 3Vdc. Refer to Figure #2 for
typical encoder connection diagrams.
Single-Ended
Differential
31 32 33 34 35 36
B
A
N
O
T
B
N
O
T
A
12
VDC
TB3
Common
31 32 33 34 35 36
B
A
N
O
T
B
N
O
T
TB3
A
Figure 2
Encoder Specifications
•
Line Driver 5Vdc or 8-15Vdc output
•
Minimum current of 10ma per channel
•
Quadrature or Pulse type
•
Single Ended or Differential
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External
Power Supply
ALLEN-BRADLEY
APPLICATION
CONSIDERATIONS
Smaller settings of parameter [Speed Ki] are associated with slower speed
recoveries. Figure 3 shows the different elements involved with speed control
through encoder feedback. Starting at the left, the motor is running at some
speed when the load is decreased. Just as the load decreases the speed
increases. The drive senses the change in speed through the encoder and
stabilizes the speed according to the setting in [Speed Ki]. Further along, the load
increases and the speed decreases. The same type of speed recovery occurs.
Later in figure 3 you can see what happens when accelerating with encoder
feedback enabled. The speed will "overshoot" before recovering according to
[Speed Ki].
Overshoot
Change in LOAD
Ki
Accelerating
Speed
Recovery
Figure 3
Figure 4 shows what happens to the speed graph when the [Speed Ki] is set
higher than in figure 3. Speed recovery is quicker.
Figure 4
Figure 5 shows when the [Speed Ki] parameter is set too high. This type of
behavior is dependent on load and frequency. Typically the drive will oscillate at
low load conditions on recovery. This is due to the speed compensation being
greater than the speed error.
Figure 5
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"S" - Curve
Figure 6 shows the effect that "S"-curve has on the speed when running in
encoder feedback mode.
Figure 6
The following parameters need to be set in order to get S-Curve to function.
Table #3
GROUP
Feature select
Feature Select
PARAMETER
S Curve Enable
S Curve Time
SETTING
"Enabled"=1/"Disabled"=0
0.00-300.00 sec
Settings in [S Curve Time] greater than [Accel/Decel Time 1/2] will result in a
fixed S-Curve thus doubling the settings in [Accel/Decel Time 1/2]. Example:
[Accel Time 1] = 5 sec, [Decel Time 1] = 10 sec, [S Curve Time] = 6 sec. Since
the 6 seconds exceeds the [Accel Time 1] the actual acceleration time will be 10
seconds (double the setting in [Accel Time 1]). The deceleration time, however,
will be 16 seconds by an adjustable S-Curve with ½ the [S Curve Time] used at
the start of deceleration then 10 seconds of linear decel, then the other ½ of the
[S Curve Time] at the end of deceleration. S-Curve is also selectable in [Stop
Select 1/2]. This causes the drive to S-Curve ramp to 0Hz by twice the setting in
[Decel Time 1/2].
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DESCRIPTION
PULSE TRAIN INPUT
The 1336 PLUS drive will accept a 5vdc pulse train input as a frequency
reference to terminals 7 and 8 of TB2. This signal is optically isolated and routed
to the microprocessor. Prior to the microprocessor, the encoder input signal “A”
joins the pulse input signal. For this reason, only one of the two inputs can be
used for any given application. Refer to figure 7.
TB2
8
Microprocessor
Isolated A
7
TB3
34
48
Isolated B
47
A
A NOT
32
B NOT
33
B
31
MOD-L4E,L5E,L6E
Figure 7
To configure the drive to use the Pulse Train Input as the frequency reference,
the parameters listed in table 4 must be programmed.
GROUP
Setup/Frequency Set
Frequency Set
Frequency Set
Encoder Feedback
PARAMETER
Freq Select 1
Freq Select 2
Pulse/Enc Scale
Pulse/Enc Scale
Table #4
TYPICAL VALUE
4
4
determined by formula
Same as above
The frequency reference that the drive will follow [Freq Select 1] or [Freq Select 2]
is determined by the logical state of the inputs to TB3 terminals 27 and 28. Refer
to table 2-H in Publication 1336 PLUS-5.0 (User Manual)
To determine the proper [Pulse/Enc Scale] value use the following formula.
Scale Factor =
Incoming Pulse Rate ( hz) Motor Poles
•
Desired Command Freq.
2
Example: 1024PPR signal from a 4 pole motor running 0-60hz. (60 x 1024)
61440 4
• = 2048
60
2
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ALLEN-BRADLEY
The pulse train input circuitry in the microprocessor uses a 1MHz clock and
several counter buffers to determine the pulse count every microsecond. Every
10msec the pulse count and time are compared with the previous values. By
using these new values, the frequency command can then be calculated.
APPLICATION
CONSIDERATIONS
•
•
•
For systems that require a digital reference and encoder feedback, several
options are available. The 1336 PLUS can except digital references via the
following options.
Remote I/O Communications Adapter
RS232/422/485 Serial Adapter using DF1/DH485 protocol
DeviceNet Communications Adapter
Example:
For a system using two or more drives in a master/slave configuration with
encoder feedback speed regulation required, Remote I/O is a solution.
The master drive can use the encoder feedback and then via Remote I/O send
the value of [Pulse/Enc Hertz], after conditioning, to the input of the slave drives
via one of the DATALINK parameters, located in the Adapter I/O group. The
DATALINK is a discrete transfer (every scan) so update times are dependent on
the PLC scan time. For faster update, use a selectable timed interrupt in the
ladder logic to immediately update the signal at predetermined intervals. Refer to
figure X for the I/O mapping. For better tracking of the master drive set the slave
drive accel and decel times to very low values (fast rate of change).
Master Drive [Pulse/Enc Hertz] Scale = 0-32767 equals zero to maximum freq.
The value when operating in the reverse direction will use the
2’s complement of the above scale (-1 to -32768).
Slave Drive Use a [Preset Speed] as the reference. The scale for the preset
speeds via a digital reference is the desired frequency times 100. For a 0-60Hz
application the scale is 0-6000.
PLC CODE
The PLC must scale the value of [Pulse/Enc Hertz] according to the values stated
above. Remember that if the master drives is operating up to 60Hz with encoder
feedback, [Maximum Speed] and [Maximum Freq] must be programmed as
described on page 2. Scaling of the [Preset Speed]parameter for the slave drive
will also change.
Formula:
32767/6000 = value sent to slave drive
This formula is only applicable to forward operation.
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