Lake Shore 372, Руководство пользователя, Страница: 82 / 214

70 c
HAPTER
3: Installation
Model 372 AC Resistance Bridge ands Temperature Controller
50
)
setting, it is limited to a maximum output current of 0.45 A, and at the 25
)
set-
ting, the maximum heater output current is 0.63 A. The compliance voltage is 23 V
minimum, but can reach as high as 28 V if the heater resistance is higher than the
nominal setting. Refer to TABLE 3-8 for the maximum current and power ratings into
different heater resistances.
3.7.2 Heater Output
Connectors A 7-pin detachable terminal block is used to connect the sample and warm-up heat-
ers to the Model 372. One 7-pin terminal block is included in the connector kit
shipped with the Model 372. This is a common connector, and additional mating con-
nectors can be purchased from electronics suppliers, or from Lake Shore as P/N 106-
765. Both the sample and warm-up heaters are connected between their resp
and - terminals.
3.7.3 Heater Output
Wiring Heater output current is what determines the size (gauge) of wire needed to connect
the heater. The maximum current that can be sourced from sample heater output is
100 mA, while the warm-up heater can source up to 0.63 A. When less current is
needed to power a cooling system, the sample heater can be limited with range set-
tings while the warm-up heater can be limited by maximum current settings.
When setting up a temperature control system, the lead wire for the heater must be
capable of carrying a continuous current that is greater than the maximum current.
Wire manufacturers recommend 30 AWG or larger wire to carry 0.63 A of current, but
there is little advantage in using wire smaller than 20 AWG to 22 AWG outside the
cryostat. Inside the cryostat, smaller gauge wire is often desirable.
It is recommended to use twisted heater leads. Large changes in heater current can
induce noise in measurement leads and twisting reduces the effect. It is also recom-
mended to run heater leads in a separate shielded cable from the measurement leads
to further reduce interaction.
For best noise performance, do not connect the resistive heater or its leads to chassis
ground. Also avoid connecting heater leads to sensor leads or any other instrument
inputs or outputs.
Heater resistance (
)
)
10 25 30 40 50 100
Maximum
current
0.63 A 4 W 10 W 12 W — — —
0.5 A (user) 3 W 6 W 8 W 10 W — —
0.45 A 2 W 5 W 6 W 8W 10 W
Shaded black: maximum current too high for these resistances due to voltage compliance limit
Bold: discrete options available for 25 ) and 50 ) heaters under the maximum current setting
TABLE 3-8 Warm-up heater resistance
FIGURE 3-15 Rear panel output terminals (without block attached)