Instrumentation Systems & Services MicroSpeed 196 User Manual Download Page 11

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In the Master mode, the correction amount is based on the formula:

In Master Mode, the correction is limited to 25% of the total output per 10 msec cycle.

In the Follower mode, the correction change is based on the formula:

Variable 13 - (I) Integral (or Reset)

The

Integral

operates as a long term

correction. It will add or subtract one DAC bit based on a positive or negative error. If
the

Integral

error is set at 100, this will happen every 20 msec. Each whole number

below 100 will add 10 msec to the loop time this bit is added.

Variable 14 - (D) Derivative (or Rate) -The Derivative

operates as a boost to the

Gain

(Variable 12). Its function is to reduce the time it takes to eliminate a large error.

In Master mode, it operates identically to the

Gain,

except it has only half the authority

to change the output. In Follower mode, it operates identically to the

Gain

with the

same authority, but is only active when the error is greater than one Follower Feedback
Sensor revolution.

Use the following steps to tune the PID Variables:

Note: Before beginning PID tuning, be sure that the Command Output has been
calibrated to the drive, and that all

ACCEL

and

DECEL

adjustments on the drive have

been set to their minimum positions. Failure to make these adjustments will degrade the
accuracy of the control.

Set Variable 13 (I) and Variable 14 (D) to zero (0).

Start the motor and set the speed to run at the most common operating speed.

Begin increasing the

Gain

(Variable 12) until instability (over and undershooting)

occurs. At this point, decrease the

Gain

until the motor stabilizes. The motor should

now be operated at different speeds throughout the operation range to ensure
stability.

Begin adding

Integral

(Variable 13) into the control loop. Keep increasing this

number until the motor begins to hunt above and below the Set Point, then back off
the number until the hunting stops.

Derivative

(Variable 14) can then be activated. Again, increase the value until

instability occurs and then back off. The most common value is usually from
50 - 100% of the value in the

GAIN

variable.

Run the the motor at all operating speeds to ensure stability. If instability occurs,
retune the PID parameters at the unstable speed.

FOLLOWER MODE PID CONSIDERATIONS:

Variable 09 - Max Lead Wind-Up -

If you are speed matching and have very fast

master speed changes, or if you are bringing the Follower motor on-line with the master
motor already running, you may want to limit the maximum error accumulated. The
MicroSpeed 196 can be programmed to make up every revolution missed, up to 9,999,
or can be limited down to one revolution. Care must be taken, however, not to limit the
error count so low, that the MicroSpeed 196 cannot hold correct speed.

Note: Most applications should leave

Max. Lead Wind-Up

at the default value of 100.

Using

the

integral? -

The MicroSpeed 196 in the Follower mode operates on a zero

error basis. For every master pulse, the MicroSpeed 196 will attempt to force a
corresponding follower pulse. The MicroSpeed 196 generates its expected analog
output based on the frequency of the lead motor. The

Gain

variable then uses error

pulses between the master and follower motor to lock the speeds together. Some phase
error between the shafts will occur. The degrees of phase error depends on the

Gain

number (Var 12) x pulses

per revolution, and the difference between the expected and

required output. If you are speed matching, a phase error is not a problem. If you need
the phases locked, you must add Integral

to the PID loop. Integral (Var 13) will add

or subtract one DAC bit (out of 4095) at the programmed rate until the error count is
zero pulses. Integral will over or under-speed the motor for the required time period.
(This is not desirable if you are only speed matching.)

Softening the Master Motor

Every system (motor, drive, gearing, and load) has a

response time i.e., the ability of the system to respond to a change in speed command.
If we demand a change that is faster than a machine’s response time, we generate error.
Often when a follower motor’s speed is erratic (jumping or lagging), the only way to

correct this is to slow down the rate of change on the master motor. This includes the
ACCEL and DECEL rates, as well as the PID on the master control. Basically, this
allows the follower control’s PID Variables the time needed to overcome the delays in
the follower system. To slow down the PID response of the master - the MicroSpeed

196 - turn the

Derivative

to zero, increase the

Integral

and reduce the

Gain

. This will

slowly

correct the lead motor’s speed.