Lake Shore Model 340 Temperature Controller User’s Manual
3-10
Installation
The Model 3003 is a passive filter and requires no
external power supply. The
High
and
Low
terminals
on the controller must be connected to the
High
and
Low
terminals marked
From Controller
on the Model
3003. The binding posts or a dual banana plug can
be used to connect to the model 3003. Precautions
must be taken to ensure the High and Low terminals
are not reversed. A diode in the Model 3003 shorts
the heater output if the polarity of the terminals is
reversed.
The
High
and
Low
terminals marked
To Heater
on
the Model 3003 should be attached to a resistive
heater used for temperature control. The binding
posts or a dual banana plug can be used to connect to the Model 3003. The ground terminals on the
Model 3003 continue the shield if the heater cable is shielded.
3.5.7 Loop 2 Output
The Model 340 has a second control loop called Loop 2. Loop 2 is an auxiliary control loop with enough
features to control a radiation shield or small sample heater. Loop 2 has a different output from Loop 1, it uses
Analog Output 2 as its actuator. It is a variable DC voltage source that can vary from -10 V to +10 V. The
resolution of the analog output is 1.25 mV or 0.0125% of full scale. The output can source up to 100 mA of
current providing a maximum of 1 W of heater power.
3.5.8 Loop 2 Output Resistance
The power delivered by the Loop 2 output is calculated as:
P
V
R
heater
=
2
The output is rated for no more than 100 mA of current, so for the maximum of 1 W output power use a 100
Ω
resistive heater with a power rating greater than 1 W. Smaller resistance values should not be used, but
larger resistances can be used for lower power applications.
3.5.9 Loop 2 Output Connector
The connector for Loop 2 output, which is Analog Output 2, is a BNC connector. The inner conductor is the
output voltage terminal, the outer conductor is attached to chassis ground inside the instrument. A coaxial
cable with attached BNC terminal is recommended for this output. The center conductor is capable of carrying
the maximum current and the outer conductor acts as a shield. It is not recommended to attach the outer
conductor to ground at the opposite end of the cable. These connectors are not included with the Model 340
but is available from local electronic suppliers.
3.5.10 Loop 2 Heater Protection
The output is short protected so the instrument is not harmed if the heater resistance is too small. It is not
recommended because the additional load on instrument power supplies causes noise on internal circuits.
The second control loop has fewer features than the first including software protection and limits. The user
must be careful to build a robust system and account for the voltage range and power up state of the control
output.
HI
FROM CONTROLLER
LO
CAUTION:
THIS HI TERMINAL
MUST BE
CONNECTED TO
HI TERMINAL OF
THE CONTROLLER
HI
TO HEATER
LO
3003 Heater Output Conditioner
Figure 3-4. Model 3003 Heater Output Conditioner