Lake Shore 350, User Manual

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4.5.1 Heater Outputs 75
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4.5.1 Heater Outputs Heater Outputs 1 and 2 are traditional control loop heater outputs for a cryogenic
temperature controller. Output 1 is designed for bulk heating and control at higher
temperatures, and can provide up to 75 W. Output 2 is designed for control at very
low temperatures, and can provide up to 1 W. They each include a large set of hard-
ware and software features making them very flexible and easy to use. The heater
outputs are well-regulated DC outputs. This provides quiet, stable control for a broad
range of temperature control systems in a fully integrated package. The power ranges
for each output provide decade steps in power.
4.5.1.1 Max Current and Heater Resistance (Output 1 Only)
The Model 350 heater output is designed to work optimally into a 25
)
or 50
)
heater. The Heater Resistance and Max Current parameters work together to limit the
maximum available power into the heater. This is useful for preventing heater dam-
age or limiting the maximum heater power into the system. When using a 25
)
or
50
)
heater, set the Heater Resistance parameter accordingly. The Max Current set-
ting will then provide multiple discrete current limit values that correspond to com-
mon heater power ratings. The available current limits keep the output operating
within the voltage compliance limit to ensure the best possible resolution. These
parameters work with the Heater Range parameter (section 4.5.1.5.8) to provide
safety and flexibility.
If you are not using a standard heater resistance, set the Heater Resistance setting to
25
)
for any resistance less than 50
)
, or to 50
)
for any higher heater resistance. The
user max current setting is useful when using a non-standard heater resistance value.
Refer to section 4.5.1.1.1 for more information on User Max Current. TABLE 4-14 pro-
vides examples of different heater resistances and max current settings, and the
resulting maximum heater power. The maximum heater powers in bold represent the
discrete current limits available under the Max Current setting for 25
)
and 50
)
heaters.
Menu Navigation:
Output Setup
Q
Output (1)
Q
Heater Resistance
Q
(25
)
or 50
)
)
Output Setup
Q
Output (1)
Q
Max Current
Q
(User, 0.707 A, 1 A, 1.414 A, or 2 A)
Default:
Heater Resistance
Q
25
)
Output 1
Q
Max Current
Q
2 A
Output 2
Q
Max Current
Q
1.414 A
Interface Command: HTRSET
4.5.1.1.1 User Max Current
When using a heater that is not 25
)
, 100 W or 50
)
, 50 W the provided discrete cur-
rent limits may not be appropriate. The User Max Current setting is available for this
case. The optimal maximum current value should be calculated based on the heater’s
power rating, or the maximum desired heater output power, whichever is lower. The
heater output compliance voltage (50 V for both heater outputs) should also be taken
into account in order to maximize heater setting resolution. This calculated current
limit can then be entered using the User Max Current setting.
To calculate the Max Current setting based on a heater or load power limit, calculate
current, I, using both of the following equations: I = Sqrt(P/R) and I = 50 V/ R where P is
the maximum allowable power, R is the heater resistance. The load power limit and
voltage compliance limit of the heater output (50 V) are in place at the same time, so
the lower calculated current is the correct Max Current setting.