Watlow Series SD31 PID with Optional Countdown Timer - Manual (Page 52)

Manual Tuning
In some applications, the autotune process may not
come up with PID parameters that provide the process
characteristics you desire. If the autotune does not pro-
vide satisfactory results, you will have to perform a
manual tune on the process:
1. Apply power to the Series SD31 and establish a
set point typically used in your process.
2. Go to the Operations Page, and establish values
for the PID parameters: Proportional Band = 5; Reset* =
0.00; Rate* = 0.00. Note: Autotune should be set to off.
3. When the system stabilizes, watch the process val-
ue. If this value fluctuates, increase the proportional
band setting until it stabilizes. Adjust the proportional
band in 3° to 5° increments, allowing time for the sys-
tem to stabilize between adjustments.
4. When the Input has stabilized, watch the percent
power , (Po.ht or Po.cl). It should be stable ±2%. At this
point, the process temperature should also be stable, but
it will have stabilized before reaching set point. The dif-
ference between set point and actual can be eliminated
with reset.
5. Start with a reset* value of 0.01 (99.99)** and al-
low 10 minutes for the process temperature to get to set
point. If it has not, double (halve) ** the setting and
wait another 10 minutes. Continue doubling (halving) **
every 10 minutes until the process value equals the set
point. If the process becomes unstable, the reset* value
is too large (small) **. Decrease (increase) ** the reset
value until the process stabilizes.
6. Increase Rate* to 0.10 minute. Then increase the
set point by 11° to 17°C. Monitor the system's approach
to the set point. If the process value overshoots the set
point, increase Rate* to 0.50 minute. Increase the set
point by 11° to 17°C and watch the approach to the new
set point. If you increase Rate* too much, the approach
to the set point will be very sluggish. Repeat as neces-
sary until the system rises to the new set point without
overshoot or sluggishness.
*With the [unit] parameter set at [SI] ( Setup
Page) Integral will appear in place of Reset and Deriva-
tive will appear in place of Rate.
**Integral is the reciprocal of reset. For Integral in-
stead of reset, use the values in parentheses.
For additional information about autotune and PID
control, see related features in this chapter.
Inputs
INFOSENSE™ Temperature Sensing
Watlow’s INFOSENSE™ feature can improve tem-
perature sensing accuracy by 50%. Watlow’s INFO-
SENSE™ thermocouples and RTD temperature sensors
must be used together to achieve these results.
Each INFOSENSE™ “smart” sensor contains four
numeric values that are programmed into the SD mem-
ory. These values characterize Watlow sensors, for the
controller to provide greater accuracy.
Turn the INFOSENSE™ feature on or off with
INFOSENSE™ Enable [IS;En] (Setup Page). Set the
four numerical values supplied with Watlow’s INFO-
SENSE™ in the
[IS;P1], [IS;P2], [IS;P3] and [IS;P4]
parameters.
Contact your Watlow salesperson or Watlow author-
ized distributor for the pricing and availability of Wat-
low INFOSENSE™ products.
The four numerical values are found on the tag at-
tached to the sensor.
Calibration Offset
Calibration offset allows a device to compensate for
an inaccurate sensor, lead resistance or other factors
that affect the input value. A positive offset increases
the input value, and a negative offset decreases the in-
put value.
The input offset value can be viewed or changed with
Calibration Offset [`CAL] (Operations parameters).
Time
Temperature
Temperature Reading
from Sensor
Actual Process Temperature
Negative Calibration Offset will
compensate for the difference
between the Sensor Reading and
the Actual Temperature
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