Lakeshore 336, Руководство пользователя

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36 c
HAPTER
3: Installation
Model 336 Temperature Controller
3.5.7 Lowering
Measurement Noise Good instrument hardware setup technique is one of the least expensive ways to
reduce measurement noise. The suggestions fall into two categories: (1) do not let
noise from the outside enter into the measurement, and (2) let the instrument
isolation and other hardware features work to their best advantage. Here are some
further suggestions:
D
Use four-lead measurement whenever possible
D
Do not connect sensor leads to chassis or earth ground
D
Use twisted shielded cable outside the cooling system
D
Attach the shield pin on the sensor connector to the cable shield
D
Do not attach more than one cable shield at the other end of the cable
D
Run different inputs and outputs in their own shielded cable
D
Use twisted wire inside the cooling system
D
Use similar technique for heater leads
D
Use a grounded receptacle for the instrument power cord
D
Consider ground strapping the instrument chassis to other
instruments or computers
3.6 Capacitance
Sensor Inputs
(Model 3061) This section provides information for a Model 336 configured with the capacitance
sensor input option card. Capacitance inputs are not installed on the standard Model
336, but it can be added by purchasing the Model 3061 capacitance input option.
Refer to section 7.6 for installation of the Model 3061.
The Model 3061 adds a capacitance input to the Model 336, appearing on the display
as input D. The card has separate voltage feedback and current excitation for the sen-
sor. The Model 3061 is intended to control temperature in strong magnetic fields
using a Lake Shore Model CS-501 capacitance temperature sensor. The standard
inputs remain in the instrument and are fully functional.
Upon changing control to the capacitive sensor, the PID values will need to be optimized.
The Model 336 does not support temperature conversion for the capacitance input.
The temperature response of capacitance sensors shifts with thermal cycling, making
calibration unpredictable. All Model 3061 option measurement and control must be
done in sensor units. With this option, two sensors should be installed at the control
point. Use a resistive sensor in one of the standard inputs to establish a control tem-
perature and stabilize the system in a low magnetic field. Before increasing the field
strength, shift control to the capacitance sensor to maintain the current
temperature.
FIGURE 3-6 2-lead sensor measurement
+
+
–
–
I
V
V
I