Lake Shore Model 340 Temperature Controller User’s Manual
5-6
Measurement Operation
5.3.3 Linear
Equation
The Model 340 can calculate a linear equation as a special data processing feature. The output of this
calculation can be shown on the display or directed to an analog output for proportional control of other
hardware in an experiment. One computation can be done for each sensor input. The output will not
automatically show on the display, use the display format setting screen described in Paragraph 4.5 to
change display settings. If an analog output is being used, its output scale must be set (Paragraph 7.1).
There are two different equations available. In each: M is a gain or slope, X is an input reading, and B is an
offset or intercept (not to be confused with input B). The two equations are shown in the table below. The
difference between them is subtle. The first equation is used to scale the raw reading of an input, similar to a
temperature response curve, when the sensor has linear response. The second is better at generating a
control signal when a setpoint (SP1 or SP2) is selected as B. The control signal can then be directed to an
analog output. The second equation is also useful whenever a reading of deviation from setpoint is needed.
The columns settings in Table 5-4 are selected
independently. “Number” represents a number entered by
the user. “X” can be set to an input reading in sensor
units or temperature in kelvin or Celsius. SP1 represents
setpoint of Loop 1 and similarly for other B settings.
To setup a linear equation, press the
Math Setup
key
and the math setting screen will appear. Press the
More
key to show the setting screen for linear equation with
the input letter in the top left hand corner. Use the
s
or
t
key to select an input. Press the
Enter
key or the
Next Setting
key to display the equation parameters for
that input. Use the
s
or
t
key to select one of the two equations from the highlighted equation field. Press
the
Next Setting
key and continue to select parameter settings for M, X, and B. A number setting field will
appear next to the field for B if number is selected from the B setting list. The scale factor can be selected as
n, µ, m, k, M, or G. Blank indicates a scale factory of x1. Press the
Save Screen
key to store the change in
the Model 340. The default settings are M(X+B), 1, K, –SP1.
5.4 SCANNER
SUPPORT
The Model 340 supports a user-supplied sensor scanner (external to the instrument). Scan up to 16 sensors
of the same type into input A. The sensors must be the same type because only one sensor type setting can
be made for the A input. Each of the 16 sensors (channels) can have a unique temperature response curve.
There are different modes of scan operation that allow for active scan channel selection. If a channel is not
actively read, the last valid reading for that channel either displays or reports over the computer interface.
Four-lead sensor measurement is always recommended when scanning temperature sensors.
5.4.1 Scan
Modes
Scanner support has different modes for selecting which of the channels is actively being read. Each mode
allows for a different scanner applications.
Manual
The user manually selects the scan channel over front panel or computer interface.
Digital outputs report the scanned channel if set to scanner mode.
Auto Scan
The instrument sequences through enabled channels, holding on each channel for a
user-specified interval. Digital outputs report the scanned channel if set to scanner mode.
Slave
The external scanner selects the channel through the digital inputs
Off
All scan functions are disabled.
To select a scanner support mode, press the
Scan
Setup
key. The Mode field will be highlighted. Use
the
s
or
t
key to select the appropriate scan mode.
Then press the
Save Screen
key. The default
setting is Off.
Equation M
X
B
MX+B
M(X+B)
Number Sensor
Temp K
Temp C
Number
SP1
–SP1
SP2
–SP2
Table 5-4. Linear Equation Configuration
M o d e :
E X T E R N A L S C A N N E R S E T U P