Wavelength Electronics LFI-3500 Series, User Manual

Page: 13 / 38

Configuration Switch Bank:
This ten position switch bank configures the type of
sensor used, the feedback P, I, and D terms, and sets the
temperature limit to a HIGH or LOW limit.
Switches 1, 2, & 3: (10
µ
A, 100
µ
A, and 1000
µ
A)
Determines reference current through the sensor. If more than one switch is ON, the
current will be the sum of the respective currents. These switches should always be
in the OFF position for AD590 sensors.
Switch Position Reference Current
1
10
µ
A
2
100
µ
A
3
1000
µ
A (1mA)
Switch 4: (AD590) In the ON position, this switch connects a 10k
Ω
resistance between
pin 5 (Sensor 1+) and pin 4 (Sensor -) on the output connector. This resistance will
create a voltage proportional to the current supplied by the AD590 sensor. This
should be in the OFF position for any other sensors.
Switch 5: (NTC/PTC) This switch determines loop polarity. Since a thermistor is a
negative temperature coefficient (NTC) sensor, the switch should be in the OFF
position when using a thermistor. The use of a PTC sensor, such as the LM335,
AD590, or RTD requires that this switch be in the ON position.
Switch 6 : (Integral Term) This switch configures the integral time constant to be either
one or ten seconds. In the OFF position, the integral time constant is one second. In
the ON position, it is 10 seconds. The larger time constant should be selected for
those loads that cannot be stabilized using the one second time constant. See page
Error! Bookmark not defined. for a discussion of the P, I, and D terms.
Switches 7 & 8: (Proportional Term) Four gain choices are available- 16, 32, 64, and
84. The following table applies:
Switch 9: (Derivative Term) The LFI can operate as a PID or PI controller. In the OFF
position, the derivative term is removed. In the ON position, a differential time
constant of 250 milliseconds is used. The D term should be selected for large or hard
to stabilize loads.
Switch 10 : (Temp Limit HIGH / LOW) The LFI can trigger an error to shut off the
output if the sensor temperature exceeds a HIGH temperature or falls below a LOW
temperature. The function of this switch changes depending on the type of sensor
used. The following table applies:
OFF
ON
2 3 4 5 6 7 9 1 10 8
CONFIGURATION
Gain Switch 7 Switch 8
16 OFF OFF
32 ON OFF
64 OFF ON
84 ON ON
Sensor Type
Temp Limit NTC PTC
LOW ON OFF
HIGH OFF ON