Lake Shore 372, Руководство пользователя, Страница: 102 / 214

90 c
HAPTER
4: Operation
Model 372 AC Resistance Bridge and Temperature Controller
4.5.2 Active Common
Mode Reduction Active common mode reduction is a special feature of the Model 372 that can reduce
noise on the measurement input leads. It is most useful when the excitation current is
1 µA or less, but it should be left on unless one resistor lead is shorted to measurement
common (section 3.5.5).
Menu navigation:
Instrument Setup
Q
CM Reduction (On, Off )
Default: On
Interface command:
CMR
4.5.3 Monitor Output
Selection The monitor output on the Model 372 is a tool to help the user diagnose measure-
ment problems. The output can be set to monitor test voltages from several points
inside the instrument. The monitor voltages are often used with the reference output.
The signal presented at the reference output is a function of the monitor point
selected. An explanation of these monitor voltages is given with other troubleshoot-
ing information in Chapter 8.
4.6 Output Control
Setup
Once the sensor inputs have been configured (section 4.4), the outputs can be config-
ured. The Output Setup menu is used to create control loops for controlling tempera-
ture, whether using feedback (closed loop) or manually setting the output (open
loop). This section describes how to operate the output and control features, and how
to set control parameters. Each control parameter should be considered before turn-
ing on a control loop output or the instrument may not be able to perform the most
simple control functions. A good starting point is deciding which control loop to use,
whether to operate in open or closed control mode and which tuning mode is best for
the application. Other parameters fall into place once these have been chosen.
Section 2.11.2 of this manual describes the principles of closed loop proportional,
integral, and derivative (PID) control.
4.6.1 Heater Outputs The Mode 372 comes equipped with two heaters. The sample heater is designed for
control at very low temperatures, and can provide up to 1 W. The warm-up heater is
designed for bulk heating and control at higher temperatures, and can provide up to
10 W. They each include a large set of hardware 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.
Monitor point Description Reference source
Off Output grounded to measurement common Measurement
CS NEG AC voltage driving negative side of current source programming resistor Measurement
CS POS AC voltage driving positive side of current source programming resistor Measurement
VCM NEG AC voltage on the negative side of the differential input amplifier Measurement
VCM POS AC voltage on the positive side of the differential input amplifier Measurement
VDIFF AC voltage output of the differential input amplifier Measurement
Measurement
A/D
AC voltage into the measurement input AD converter Measurement
Control AC voltage into the control input AD converter Control
TABLE 4-9 Monitor output voltages