a103_02General brochure.pdf

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Electric Actuators
A103/02
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SUMMARY
BERNARD classification
3
Terminology
4
Motor duty service
5
2
Positioning loops
6
Regulation modes
7
3 classes of actuators
8
Electronic positioner general functions
10
Specialized positioners
1 1
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Bernard modulating classification
A modulating actuator has to be fully adapted to the
duty given by the modulating loop. According to the
duty or the functionning frequency, the actuator
technology and its cost will be different : a choice has
to be done within our 3 classes of modulating
actuators.
CLASS III
CLASS II
CLASS I
CLASS III POSITIONING
n
l
The actuator is able to reach an intermediate
position with a sufficient precision (better than 2%).
CLASS III
l
The motor is able to start 1200 times per hour with
a duty cycle of 50%, as to say a start every 3
seconds. This starting frequency allows the process
to stabilize a position, but shall not be kept
permanently.
Open
Close
l
A Class III actuator is designed for an average of
360 change of position a day.
Technology : A Class III actuator is selected in the
On/Off actuators range.
Remark : If you need to use the actuator with an other
behaviour, please consult us.
Time
CLASS II PRECISION POSITIONING
3
n
l
The actuator is able to reach an intermediate
position with a good precision (better than 1%).
CLASS II
l
The motor is able to start 1800 times per hour with
a duty cycle of 100%.
Open
l
A Class II actuator is designed to move
permanently each 2 or 3 seconds.
Technology : Actuator with high mechanical efficiency,
special modulating motor, solid state relay control.
Close
Time
CLASS I FAST POSITIONING
n
l
The actuator is able to reach an intermidiate
position with a precision of 0,5% or better..
CLASS I
l
The actuator can move the valve, full stroke, very
quickly.
Open
l
A Class I actuator is designed to move
permanently.
Technology : Actuator with high mechanical efficiency,
brushless electric motor with speed regulation.
Includes PWM (Pulse Width Modulating) power
electronics.
Close
Time
Criterias
CLASS III
CLASS II
CLASS I
Modulating type
POSITIONING
PRECISION POSI.
FAST POSITIONING
Precision of positioning
< 2%
< 1%
< 0.5%
Max number of starts per hour
1200
1800
No limits
Operating duty cycle
50 %
100 %
100 %
Start : average for a day
360
not applicable
not applicable
Positioning of a critical or unstable system
Unadvised
Yes
Yes
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Terminology
PRECISION OF POSITIONING
This is the maximum deviation between the real
position and the theoretical position, given as a
% of the total stroke.
TYPE TEST
n
Signal
Theoretical Actual
Devia-
Hyste-
mA
position position
tion
resis
4
0
0,0
0,0
0,1
8
25
25,1
0,1
0,4
OPEN
12
50
50,0
0,0
0,2
HYSTERESIS
This is the maximum deviation between the
position achieved from rotation to open and the
same position achieved from rotation to close,
as a % of the full stroke.
n
direction
16
75
75,2
0,2
0,3
20
100
100,0
0,0
--
16
75
74,9
0,1
CLOSED 12
50
49,8
0,2
As an example, partial test results are published
in the table on the right to appreciate the "
precision and hysteresis ".
direction
8
25
24,7
0,3
4
0
-0,1
0,1
Precision
max. deviation
0,3%
Hysteresis
max. deviation
0,4%
RESOLUTION
This is the actuator movement obtained by the
smallest possible input signal. The maximum
value is given as a % of the full stroke.
n
4
DEAD BAND
The dead band is an adjustable value at the
positioner. If the deviation between the signal
and position is less than the dead band, the
actuator will not move. Adjustment of the dead
band is made to obtain the best compromise
between precision and position (narrow dead
band) and non-hunting of the actuator (large
dead band).
n
OPERATING TIME
This is the time the actuator needs to achieve a
full stroke. Electric actuators provide the same
operating time in opening and closing direction.
n
n STABLE SYSTEM, OCCASIONALLY
UNSTABLE SYSTEM OR UNSTABLE
SYSTEM
In electric modulating duty the motor has to
withstand multiple starts, stops and changes in
direction of rotation. For this, it is essential to
know what working conditions are present
before choosing the actuator.
RESPONSE TIME
Is the time the actuator requires to travel to the
requested position. To simplify, the operating
time of the full stroke is taken into consideration.
n
The actuator travels to a position and may stay
there several minutes without changing position.
The displacements are of minor amplitude.
Changes in direction of rotation are infrequent.
MOMENTARY AVAILABLE
TORQUE, PERMANENT MAXIMUM
ADMISSIBLE TORQUE
To size the actuator, the two torques must be
taken into consideration. Momentary torque is
used for close tight operation. This torque is
provided but should not be used for modulating
duty. Permanent torque is the maximum torque
the actuator can work in regulation.
n
The actuator position may occasionally change
due to external interference.
Frequent variations of positioning values
requires the actuator to work with large and
sustained movements.
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Motor duty service
OPERATING CONDITIONS
n
l
S7 : Periodic continuous duty with
electrical braking
- Identical to S5, but without rest period.
l
S1 : Continuous duty
- Continuous operation at load over sufficient
time for thermal equilibrium to be reached.
l
S8 : Continuous operation periodic duty
with related change of load and speed
- Identical to S7, but with different rotation
speeds.
l
S2 : Short time duty
- Allows a sufficient rest period between
operations for the motor to cool down.
l
S9 : Duty with non-periodic variations in
load and speed
l
S3 : Intermittent periodic duty
- Starting current does not significantly effect
the temperature rise.
- Maximum operating time to be specified.
l
S10 : Operation at discrete constant loads
- This duty consists of a maximum of 4 discrete
load values (or equivalent loads), each value
being applied for sufficient time to reach
thermal balance.
l
S4 : Intermittent periodic duty with starting
- Repetition of cycles consisting of :
• starting period D,
• period of operation at constant load N,
• rest period R.
5
APPLICATION FOR ACTUATORS
Actuators operate at S4 type of duty which
requires that duty rating and the number of starts
per hour be mentioned to complete operating
conditions.
n
For ON-OFF applications, number of starts per
hour may be low but the operating time long,
therefore the motor temperature rise is mainly
influenced by the duty cycle.
For modulating applications number of starts per
hour may be high but the operating time short,
therefore the motor temperature rise is mainly
influenced by the number of starts/hour.
- To be followed by the duty rating in % :
M
M + R
x 100
as well as the number of starts per hour
l
S5 : Identical to S4, but with electrical
braking
l
S6 : Periodic continuous duty with
intermittent load
- Continuous operation with intermittent load.
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