Wavelength Electronics LFI-3751 User manual

LFI-3751 with Autotune PID
Thermoelectric Temperature Controller
Key Features . . .
•< 0.002°C temperature stability even at ambient
•Controls temperature with thermistors, RTDs, LM335, or AD590
The LFI-3751 with Autotune PID is a high performance
temperature controller specifically designed for sensitive
applications. Now with Autotune PID capability, the
LFI-3751 automatically optimizes virtually any thermal
load; reduce overshoot or improve temperature stability
with the push of a button.
. . . The Wavelength Advantage
Autotune PID
PID Constants adjustable via front panel
Auto-ranging thermistor & RTD bias current
Bipolar or Unipolar output current operation
High and Low Temperature Limits
Auxiliary temperature sensor input
Analog input allows for external temperature control
(Analog model only)
Addressable RS-232 interface
LFI3751-00400-C Rev D

The Front Panel at a Glance
2
2
1
mV / K
SENSOR
avelength Electronics
5 Amp - 40 Watt
Temperature Controller
BA
POWER
LM335
AD590
Thermistor T , R
3, 3
2, 2
1, 1
RTD
11T , R
2
1
A / K
µ
T , R
HOLD FOR LOCAL
RS-232
C
T , R
mV offset
A offset
T , R
µ
3
2
3
2
W
AMPS
RS-232 ADDRESS
VOLTS
ON
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
ERROR
°C
k
HOLD SHIFT FOR
OUTPUT
SHIFT
MODEL LFI-3751
STATUS
TEMP LIMIT
REMOTE
T LIMIT LIMIT I
SENSOR
Off
On
Status Section
4 Digit Display
Display
Select
Switch
Sensor
Reference
Section
AC Power Switch
Digi-Pot
Adjust Knob
Display
Section
Units of
Measure
Shift Button
Output Section
}
Temp Limit
Button
Output Button

3
While displayed, Parameter
can be changed by rotating
Digi-Pot Adjust Knob
Digi-Pot Adjust Knob
is disabled. Monitor
parameter only.
LED is OFF
LED is lit SOLID
LED FLASHES
Front Panel Operations at a Glance
Operation Legend
Adjusting Limit Current
Rotate the Display Select Switch to LIM I.
Positive Limit Current (0 to +5 Amps) will
alternate with the Negative Limit Current
(-5 to 0 Amps).
LIMIT I LIMIT I LED flashes:
TE Current is limited by
LIM I settings.
WAIT - Most thermal loads require maximum
current while initially controlling to temperature.
To control properly, the output current must be
less than the LIM I current setting.
CAUTION: Improperly set LIM I
can damage your thermoelectric
Limit Current LED
ERROR
SENSOR
ON
OUTPUT
IS SENSOR
ERROR CONDITION
CORRECTED?
BEEP
ON
OUTPUT
3
BEEPS
LONG
BEEP
IS SENSOR
ERROR
CONDITION
CORRECTED?
NO
YES
YES
NO
PRESS
OUTPUT
BUTTON
SENSOR ERROR LED
flashes: Sensor is either
OPEN or SHORTED. Output
forced OFF.
Press Output Button to
re-enable output current.
Press Output Button
to clear error.
Sensor Error LED & Correcting the Sensor Error
T LIMIT
ON
OUTPUT
OVER / UNDER
TEMPERATURE
CONDITION
CORRECTED?
ON
OUTPUT
BEEP
3
BEEPS
LONG
BEEP
OVER / UNDER
TEMPERATURE
CONDITION
CORRECTED?
YES
NO
YES
NO
PRESS
OUTPUT
BUTTON
T LIMIT LED flashes:
Sensor temperature is
outside temperature
limits. Output is disabled.
Press Output Button to
re-enable output current.
Press Output Button to
clear error.
Temperature Limit LED & Correcting the Temperature Limit Error
Press &
Release
TEMP LIMIT
TEMP LIMIT 1
°C°C
TEMP LIMIT 2
(Cycles three times, then reverts to prior display)
T LIMIT
Adjusting Temperature Limits : -199.9 to +199.9°C
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
Negative LIM I
Positive LIM I
Note: Temperature Limit does not
operate in Resistance Mode for
thermistors or RTDs.

4
ONON PRESS &
RELEASE
PRESS &
RELEASE
ON
Output Current
Disabled
Output Current
Enabled
Output Curren
t
Disabled
Enable / Disable Output Current
Press & Hold
for more than
3 seconds
TEMP LIMIT
BUTTON
RS-232
REMOTE
RS-232
REMOTE
OPERATE VIA
RS-232
REVERT TO
LOCAL OPERATION
Revert to Local Mode Operation
RS-232
REMOTE
BEEP
REMOTE RS-232 LED flashes,
unit BEEPS:
RS-232 communication is
initiated and the port is active.
A flashing RS-232 LED indicates active communication
between computer and instrument
Remote RS-232 LED
A solid RS-232 LED indicates the instrument is under
remote RS-232 control, but communication between
computer and instrument is not active.
RS-232
REMOTE
SHIFT
BEEP BEEP
Continuously
Hold the Shift
Button
After 3 seconds, REMOTE RS-232
LED lights solid red, unit beeps.
RS-232 Address
Displayed while Shift
Button is held. When
Button released, new
address (if changed) is
saved and unit beeps.
Adjusting RS-232 Address
TEMP LIMIT
BUTTON
Remote RS-232
Operation
Output shuts off,
Unit remains in
RS-232 operation
Press and Hold
TEMP LIMIT and Press
OUTPUT BUTTON to
shut output off
OUTPUT
OUTPUT
RS-232
REMOTE
RS-232
REMOTE
ON
Enable / Disable Output Current During Continuous RS-232 Operation

5
The Front Panel at a Glance
Quick Autotune PID Operation
Quick Autotune PID Operation
Step 1. Adjust the Limit Current below the rated
maximum current for your thermoelectric or
resistive heater.
Step 2. Adjust the Temperature Setpoint to your desired
operating temperature.
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
Negative LIM I
Positive LIM I
(-5.00 to 0.00 Amps)
decrease
increase
(0.00 to 5.00 Amps)
Ω
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
°C
k
temperature (°C)
or resistance (kΩ)
displayed
-199.9˚C to +199.9˚C
or
0 to 500 kΩ
decrease
increase
Continued next page...

6
Step 3. Adjust the P term to display AutS or Autd.
AutS: Setpoint Response Optimization
Autd: Disturbance Rejection Optimization
(Wait about two seconds before enabling the
output current.)
Step 4. Begin Autotune Optimization: Enable Output
Current.
The time to complete an Autotune optimization
sequence varies from load to load. While tuning,
the ON LED will flash. When complete, the
LFI-3751 beeps once and the ON LED lights solid.
Three audible beeps indicate if the Autotune
sequence is aborted. The ON LED is not lit. If the
actual sensor temperature exceeds the high or low
temperature limits the optimization will abort.
See Page 23 for more detail on the LFI-3751
Autotune feature.
The Front Panel at a Glance
Quick Autotune PID Operation
Quick Autotune PID Operation, continued
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
decrease
increase
AutS or Autd (below 0)
ON PRESS &
RELEASE
ON
Output Current
Disabled
Autotune
Optimization
in Progress,
ON LED flashes
Autotune
Complete
BEEP
Phase 1: The LFI-3751 ramps the thermoelectric
current to drive the load toward the setpoint
temperature.
Phase 2: The LFI-3751 performs three characterization
passes.
Phase 3: The LFI-3751 reverts to normal operation,
saving the optimized P, I, and D settings in
non-volatile memory and settling in at the
setpoint temperature.
Ambient
Phase 1
First
Pass
Setpoint
Phase 2 Phase 3
Second
Pass
Third
Pass
Autotune Process

7
Thermistors or
RTDs (T, R) data
[C1]
[C2]
Thermistors or
RTDs (T, R) data AD590, LM335,
Slope
[B1] only
[B1]
[B2]
[A1]
[A2]
OFF (0)
OR
1 to 100 secs.
OFF (0)
OR
0.4 to 10.0 secs.
AutS or Autd
(Autotune PID)
or
1 to 100 Amps / Volt
°C
k Ω
°C
k Ω
°C
AD590, LM335,
Offset
[C1] only
k Ω
I
D
B
C
SHIFT
OFF
-8.00°C to +150.00°C
(typical)
AMPS
POSITIVE
NEGATIVE
AMPS
-12.0 to +12.0 Volts VOLTS
-199.9°C to +199.9°C
OR
0 to 500 k Ω
- 5.00 to +5.00 Amps AMPS
-199.9°C to +199.9°C
OR
0 to 500 k Ω
°C
k Ω
OR
OR
°C
k Ω
°C
PACT T
SET T
TE I
LIM I
AUX T
0.00 to +5.00 Amps
-5.00 to 0.00 Amps
TE V A
SHIFT
ON
Thermistor
RTD
AD590
LM335
10°C
1
2
3
25°C
0°C
1 µA / K
10 mV / K
19.9 kΩ
1
2
3
10 kΩ
0.100 kΩ
-
-
40°C
100°C
0 µA
0 mV
5.326 kΩ
0.139 kΩ
-
-
Default Sensor Configuration
The Front Panel at a Glance
Displaying and Adjusting Values on the Front Panel
Display Section
A B C
Sensor Type [A1] [A2] [B1] [B2] [C1] [C2]

Rear Panel at a Glance
115/230 VAC, 50/60 Hz, 160 VA
CAUTION
Do Not Open
Risk of Electrical Shock
Ne Pas Ouvrir
Risque d’ Electrocution
ATTENTION
VORSICHT
Hochspannung
Nicht ffnen
MADE IN USA
SELECT:
(5x20mm SLO BLO)
FUSE (250V):
2000 maT @ 115V
1000 maT @ 230V
Wavelength Electronics
Bozeman, Montana USA
OUTPUT
8F0-2995S/N
LINE:
ANALOG
INPUT
RS-232 OUTPUT
RS-232 INPUT
115V
Analog Input
BNC Connector
Output
Connector
(9 pin male
D-sub plug)
RS-232 Input
Connector
(25 pin female
D-sub receptacle)
RS-232 Output
Connector
(25 pin male
D-sub plug)
AC Voltage
Select Switch
Do not change this
setting while power is
supplied to the unit.
AC Fuse
For 115 VAC operation, install a 2000 maT 5 x 20 mm SLO BLO fuse
For 230 VAC operation, install a 1000 maT 5 x 20 mm SLO BLO fuse
AC Power
Entry Module
Use only the power cable
provided. Ensure that the
power source you plug
the LFI-3751 into is
properly grounded.
!
1
9
Serial
Number
Fan Vent Holes
Do Not Block or place
any objects within 6" of
the rear panel of
this instrument.
1
25 25
1
13 13
14 14
Earth Ground
If your AC power system
does not bring earth
ground through the
AC Power Entry Module,
connect earth ground
via a 16 AWG wire to
this screw terminal.
5
6
8
1
2
3
4
5
6
7
8
9
TEC +
TEC -
Aux Sensor +
*Sensor -
Main Sensor +
AD590 Voltage
*Fan -
*Fan+ (+12 V)
*-12 V
2
3
7
5, 6, 8, & 20 shorted
All other pins are floating
Instrument Receive (In)
Instrument Transmit (Out)
Signal Ground
2
3
7
All other pins are floating
Peripheral Transmit (Out)
Peripheral Receive (In)
Signal Ground
Output
9 pin male D-sub plug
RS-232 Input
25 pin female D-sub receptacle
RS-232 Output
25 pin male D-sub plug
*Thermally Fused to 100 mA

9
In This Book
Quick Start. Chapter 1 prepares the temperature controller for
use and familiarizes you with a few of its features.
Front Panel Operation. Chapter 2 details the features and
functions of the front panel. You will find this chapter useful
whether you are operating from the front panel or from the
RS-232 interface.
Rear Panel Operation. Chapter 3 details the rear panel
features and connector pin outs.
Remote Interface Reference. Chapter 4 details the RS-232
commands and responses. Remote interface programs are
provided to help you develop programs for your temperature
control application.
Specifications. Chapter 5 lists the temperature controller
specifications.
If your LFI-3751 fails within one year of purchase, Wavelength
Electronics will repair it free of charge. If you have questions
relating to the operation of the LFI-3751, you can contact
Technical Support:
Call [phone] in the U.S.
Fax [phone]
email [e-mail]
If you have purchased the controller from an international
distributor, please contact them for technical support or
repairs.

10
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Table of Contents
11
Table of Contents
Chapter 1: Quick Start.................................................................................... 13
Preparing the Temperature Controller for Use ..................................................................15
Nine Steps to Operating the LFI-3751 ................................................................................17
Chapter 2: Front Panel Operation ................................................................. 21
Autotune PID Operation.......................................................................................................23
Theory of Autotune PID ......................................................................................................30
Controlling Temperature with Thermistors ........................................................................35
Controlling Temperature with RTDs ...................................................................................39
Controlling Temperature with an AD590 ............................................................................45
Controlling Temperature with an LM335 ............................................................................48
Controlling Temperature with an LM35 ..............................................................................51
Sensor Error Condition........................................................................................................55
Setting Limit Currents..........................................................................................................56
Setting Temperature Limits .................................................................................................57
Manually Setting the P, I, and D Constants .......................................................................58
Setting Operating Temperature or Resistance ..................................................................60
Enabling Output Current .....................................................................................................61
Measuring Thermoelectric Current and Voltage ................................................................62
Measuring Auxiliary Thermistor Temperature....................................................................63
Setting the RS-232 Address ................................................................................................66
Operating with Resistive Heaters .......................................................................................67
Chapter 3: Rear Panel Operation .................................................................. 69
Connector Pinouts ...............................................................................................................71
BNC Connector.....................................................................................................................73
AC Power...............................................................................................................................74

12
Table of Contents
Chapter 4: Remote Interface Reference ....................................................... 75
RS-232 Interface Configuration...........................................................................................77
RS-232 Command and Response Packet Formats ...........................................................80
Standard Command Code Listing .....................................................................................82
Calibration Command Code Listing ..................................................................................85
Diagnostic Command Code Listing...................................................................................86
End Code Listing..................................................................................................................87
Starting RS-232 Communication with the LFI-3751 ..........................................................89
Configuring the Sensor .......................................................................................................90
Measuring Actual Temperature or Resistance...................................................................94
Setting the Limit Currents ...................................................................................................95
Setting Temperature Limits .................................................................................................96
Autotune PID & Setting the P, I, and D Constants .............................................................97
Setting Temperature Setpoint..............................................................................................99
Setting Resistance Setpoint................................................................................................100
Enabling and Disabling the Output Current ......................................................................101
Measuring Thermoelectric Current and Voltage ................................................................102
Measuring Auxiliary Sensor Temperature..........................................................................103
Setting Gain for Analog Input Signal (Rear Panel BNC Connector) ................................104
Checking the Alarm Status..................................................................................................105
Halting the Processor ..........................................................................................................106
Reverting to LOCAL Mode...................................................................................................107
Entering the PASSWORD.....................................................................................................108
Reading Serial & Model Numbers, Firmware Version .......................................................109
Calibration - Sensor Bias Current and AD590 Sense Resistance ...................................110
Calibration - ACT T, TE I,TE V uncalibrated voltages ........................................................112
Calibration - Measurement Slopes & Offsets ....................................................................113
Calibration - SET T Slopes & Offsets..................................................................................115
Calibration - TE Limit Current Slopes & Offsets................................................................116
RESTORE Calibration Defaults ...........................................................................................117
Diagnostic - Lamp Control ..................................................................................................118
Diagnostic - Switch Status ..................................................................................................119
Diagnostic - Digi-Pot Status ................................................................................................120
End Code Reference ............................................................................................................121
Calculating FCS....................................................................................................................123
Example BASIC Control Program for IBM PC Compatible Machines..............................124
Chapter 5: Specifications .............................................................................. 127
General Specifications.........................................................................................................129
Electrical Specifications......................................................................................................129
Mechanical Specifications...................................................................................................130
Appendix:
CAT-220 Cable Accessory Diagram ......................................................... 133

1
Chapter 1: Quick Start
13
1

Quick Start
This chapter shows how to set up an LFI-3751. Become
familiar with the temperature controller by following the
Nine Steps to Operating the LFI-3751 for a thermoelectric
load with a 10 kΩthermistor temperature sensor. Later
chapters expand on this information and offer complete
reference information.
14
Chapter 1 - Quick Start

One power cord
9 pin D-Sub receptacle (solder cup) and metal hood
AC fuses (Two each for 115V or 230V operation)
50 ΩBNC terminator (Analog version only)
Certificate of Calibration
5This User’s Guide
Benchlink software (3.5” floppy included with this User’s Guide)
Preparing the Temperature Controller for Use
A Verify you have received these items.
The following steps help you verify the temperature controller is ready for use.
B Verify the power line voltage setting.
Remove power cord. Change
switch to proper voltage.
Remove fuse holder assembly
and verify fuse rating or install
proper fuse.
CConnect power cord and power on the LFI-3751.
Chapter 1 - Quick Start
Preparing the Temperature Controller for Use
15
1
Ensure the power source you plug the temperature controller into is properly
grounded. Once the AC Power Switch on the front panel is pressed in,
all LEDs on the front panel will light up while the temperature controller
performs its power-on self test. After the test, the temperature controller
is ready for normal operation.
The line voltage is set to the proper value for your country when the
temperature controller is shipped from the factory. The available settings
are 115 or 230 VAC. If the voltage setting is incorrect, change it and check
that the correct fuse is installed. If fuses are not available locally, call
the Wavelength Electronics Technical Support Group or your international
distributor to order new fuses.
If anything is missing, contact Wavelength Electronics or your nearest
international distributor.
115V 230V
OR
Remove with
a screwdriver
2000 maT for 115 V
1000 maT for 230 V
5 x 20 mm SLO BLO

EIf the temperature controller does not turn on.
F
DPerform a complete self test.
Chapter 1 - Quick Start
Preparing the Temperature Controller for Use
If the controller fails step D or still does not turn on.
16
The complete self test is a more extensive set of tests than those performed
at power-on. Hold down the Shift Button as you power the unit on with
the AC Power Switch. A complete self test will start after holding the
Shift Button for three seconds. If the self test is successful, “PASS”
is displayed. If the self test is not successful, “FAIL” is displayed. If
“FAIL” is displayed, see Step F for information on returning the unit to
Wavelength for repair.
Verify that there is AC power to the temperature controller. First, check that
the AC Power Switch is in the ON position. Also, make sure the power cord
is firmly plugged into the Power Entry Module on the rear panel. Check
that the fuse in the rear panel fuse holder is in place and functional. You
should also make sure that the power source you plugged the temperature
controller into is energized.
Call your nearest Wavelength Electronics sales office for instructions
on returning the temperature controller to Wavelength for service.
In North America, call the factory directly at [phone],
Fax to [phone], or email Customer Service at
[e-mail]. If you live outside North America, contact the
international distributor you purchased the unit from.

1
T= χ1+ χ2ln(R) + χ3(ln(R))3
Chapter 1 - Quick Start
Nine Steps to Operating the LFI-3751
These nine basic steps will familiarize you with the LFI-3751
temperature controller. This example controls a thermoelectric load
to 25°C using a 10 kΩthermistor. Complete details are included
in later chapters.
Nine Steps to Operating the LFI-3751
1
9
245
Thermoelectric
(1 Amp, 3 Volt)
Thermistor
(Wavelength # TCS-610)
1
+-
Make sure
all connections
are solid.
This 9 pin D-Sub male plug requires a mating female
receptacle. Wire the thermoelectric module to pins 1
(positive lead) and 2 (negative lead). Wire the sensor
(a thermistor in this example) to pins 4 & 5. The
remaining hookups are optional. If you need a fan to
cool a heatsink, wire a +12 V fan (100 mA maximum)
to pins 8 & 7. If you need a second sensor to monitor
an auxiliary zone (ambient, heatsink...) wire a 10 kΩ
thermistor to pins 3 & 4. Install the 50 ΩBNC terminator
on the Analog Input BNC on the rear panel.
Wire Output Connector
The change in resistance vs. temperature of a thermistor can be modeled
by the Steinhart-Hart Thermistor equation. The LFI-3751 calculates the
three coefficients (χ1, χ2, & χ3) from three (Temperature, Resistance) data
pairs that you enter. Using the Steinhart-Hart equation, the temperature
controller converts the thermistor resistance to a displayed temperature.
Calibration is more accurate when the data pairs are close to the desired
operating temperature. For this example, 25°C is the goal. Calibrating
this 10 kΩthermistor with 10°C, 25°C, and 40°C will offer a wide range of
operation as well as 0.01°C accuracy.
Rotate the Display Select Switch to Aand toggle the Shift Button ON.
A temperature and a resistance will alternate on the display. See the unit
of measure LEDs to determine if it is the temperature or resistance value.
For the 10 kΩthermistor in this example, we choose A, B, and Cto be
(10°C, 19.9 kΩ), (25°C, 10 kΩ), and (40°C, 5.326 kΩ) respectively. This
information is available from the thermistor manufacturer (usually in table
form). Use the Digi-Pot Adjust Knob to change either value when it is
displayed. Rotate the Display Select Switch to Bthen C, making any
necessary adjustments.
Configure Sensor
2
Output Connector
9 pin D-sub plug (male)
PINOUT
1
2
3
4
5
6
7
8
9
TEC +
TEC -
Aux Sensor +
*Sensor -
Main Sensor +
AD590 Voltage
*Fan -
*Fan + (+12 V)
*-12 V
17
1
Steinhart-Hart Thermistor
Equation
Graph of Resistance vs.
Temperature for TCS-610
10 kΩThermistor
T = Temperature (Kelvin)
R = Resistance (Ohms)
*Thermally Fused to 100 mA
1
0
5
10
15
20
25
30
35
0 1020304050
Temperature °C
T1, R1
T2, R2
T3, R3
Resistance kΩ

Rotate the Display Select Switch to SET T and toggle the Shift Button
OFF. The setpoint temperature is displayed. Rotate the Digi-Pot Adjust
Knob until 25°C is displayed.
Display and Adjust Setpoint Temperature
5
Set Temperature Limit
4
Press and release the TEMP LIMIT Button. Two numbers will alternate
on the display. If the thermistor temperature exceeds these limits, the
output current will be turned off. The numbers will alternate three times
before the display reverts to the parameter selected by the Display Select
Switch, in this case, LIM I. Assume that the load should not be allowed
to freeze (0°C) and should not exceed 55°C. Rotate the Digi-Pot Adjust
Knob until 0°C and 55°C are displayed. The highest temperature is
selected as the High T LIMIT and the lowest temperature is used as
the Low T LIMIT.
Chapter 1 - Quick Start
Nine Steps to Operating the LFI-3751
Set Limit Current
3
With the output off, set the limit current below the thermoelectric’s
maximum current. Assume the example thermoelectric’s maximum
current is 1.25 Amps. Set the Limit Current to 1.0 Amps. Rotate the
Display Select Switch to LIM I with the Shift Button OFF. The positive
and negative limits will alternate on the display. Rotate the Digi-Pot
Adjust Knob until 1.00 and -1.00 alternate.
HOLD FOR LOCAL
RS-232
RS-232 ADDRESS
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
ERROR
°C
HOLD SHIFT FOR
SHIFT
STATUS
TEMP LIMIT
REMOTE
T LIMIT
LIMIT I
SENSOR
RS-232 ADDRESS
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
°C
HOLD SHIFT FOR
SHIFT
REPEATS 3 TIMES
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
°C
18
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
Negative LIM I
Positive LIM I

Rotate the Display Select Switch to TE I (Shift Button OFF) to monitor
the current flowing through the thermoelectric. Rotate the Display Select
Switch to TE V (Shift Button OFF) to monitor the voltage across the
thermoelectric.
Begin Autotune Optimization
6
Autotune: Rotate the Display Select Switch to Pand toggle the Shift
Button ON. Use the Digi-Pot Adjust Knob to change the value. To begin
Autotune optimization, adjust the P value to display AutS or Autd.
AutS: Setpoint Response Autotune Optimization
Autd: Disturbance Rejection Autotune Optimization
You determine what kind of control loop the Autotune will use based on
your settings for the I and D terms. If set to zero, that control term
will not be used. The following chart shows which control modes are
available and the appropriate I and D settings. Rotate the Display
Select Switch to Ithen D, making any necessary adjustments with the
Digi-Pot Adjust Knob.
For this example, adjust P to AutS, I to 1.0, and Dto 1.0 .
Manual setting: Adjust P to a value other than AutS or Autd.
Enable the Output Current
Press the Output Button to enable the output current and begin the
Autotune optimization sequence. The ON LED indicator will flash while
Autotune optimization is in progress. Once the Autotune sequence is
finished, the LFI-3751 will control to the desired operating temperature
entered in Step 5. Refer to Chapter 2, Autotune PID operation for
more detail.
Measure Actual Temperature
8
Rotate the Display Select Switch to ACT T (Shift Button OFF) to
monitor the load temperature. ACT T temperature now approaches
the SET T temperature.
Measure Thermoelectric Current and Voltage
9
Chapter 1 - Quick Start
Nine Steps to Operating the LFI-3751
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
ON
OUTPUT
19
1
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
°C
7
PACT T
LIM I
AUX T
TE V
SET T
TE I
B
C
I
A
D
AMPS
VOLTS
or
Control Mode:
PID
PI
PD
P
I
non-zero
non-zero
OFF = zero
OFF = zero
D
non-zero
OFF = zero
non-zero
OFF = zero

20
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