Wavelength Electronics LFI-3500 Series, User Manual

Page: 32 / 38

32
Analog Interface
Pins 1 & 2: (Mod+, Mod-) An external analog signal can be directly connected to
these pins (or the Analog BNC Input) to remotely control temperature setpoint.
This input is configured to accept
±
10 V signals while withstanding inputs as
large as
±
40V. Any input on these pins is directly summed with the temperature
setpoint determined by the Adjust Potentiometer. Pins 1 & 2 are isolated from
the BNC Connector via 1k
Ω
resistors. This is to protect from accidentally
connecting two separate modulation input sources in parallel. The impedance of
this input is 60k
Ω
as measured across these terminals. A total of 30k
Ω
isolates
these inputs from pins 4 (Sensor -) and 7 (Fan Ground) on the Output
Connector. See the Transfer Function Table on page 33 for analog input
transfer functions.
NOTE!
The shield side of the Analog BNC input is chassis grounded. Depending on
how the thermistor or thermoelectric is grounded, three options are available:
1. If the analog inputs are not used, install the 50
Ω
terminator (provided with the unit)
on the BNC input.
2. If the thermistor or thermoelectric is not earth grounded, remove the 50
Ω
BNC
terminator. The signal can be input through either the Analog Input BNC or the
Analog Interface Connector.
3. Only the Analog Input BNC may be used for controlling the temperature when
the thermistor or thermoelectric is earth grounded. Remove the 50
Ω
BNC
terminator and replace it with the external modulation source.
Pins 3 , 4, & 15: (Boost+, Boost-, Monitor Common) These pins provide true
differential buffered outputs that can be used to drive an external power amplifier
to “boost” the power output of the controller. In this case, the thermoelectric is
connected to the booster power amplifier while the LFI controller provides the
PID temperature control. This signal is extracted from the PID section before the
current limit section. Either B or BOOSTER - can be referenced to
the MONITOR COMMON to provide the proper polarity to the external amplifier
for correct current flow through the thermoelectric. If B and
BOOSTER - are directly connected to the external amplifier, the amplifier’s gain
must be reduced by a factor of two since BOOSTER - is the complement of
B.
Thermoelectric current and voltage must be monitored using the
external power amplifier electronics.
Pins 5 & 6: (Error+, Error-) These outputs were designed to connect to the
LFI-4500 series laser diode drivers. Complementary inputs on the laser diode
drivers are located on the LFI-4500 analog interface connector. Any LFI-4500
laser diode driver connected via these error lines will be disabled if the
temperature controller output is turned off for any reason (Output On Button or
Error shutoff). These outputs can source a maximum of 10 mA of current and a
total of three LFI-4500 laser diode drivers can be connected at one time.
Pins 7 & 9: (Error Detect, Common) This output is an open drain connection that
remains in a high impedance state while there are no errors that disable the
output. If an error occurs that disables the output, this output is forced into a low
impedance state with respect to the common connection (pin 9).
LFI-4500’s output will NOT be disabled if
the LFI-3500 is in its powered off state
via its AC Power Switch.
If the thermistor or thermoelectric is earth
grounded - only the Analog Input BNC may
be used for remote control.
NOTE!