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7012 Calibration Bath
User's Guide
10.4
10.4.1
10.4.2
56
may be used. Commands may be abbreviated to the minimum number of letters
which determines a unique command. A command may be used to either set a
parameter or display a parameter depending on whether or not a value is sent
with the command following a "=" character. For example "s"<CR> will return
the current set-point and "s=50.00"<CR> will set the set-point to 50.00
degrees.
In the following list of commands, characters or data within brackets, "[" and
"]", are optional for the command. A slash, "/", denotes alternate characters or
data. Numeric data, denoted by "n", may be entered in decimal or exponential
notation. Characters are shown in lower case although upper case may be used.
Spaces may be added within command strings and will simply be ignored.
Backspace (BS, ASCII 8) may be used to erase the previous character. A termi-
nating CR is implied with all commands.
Power Control Functions
The digital interface is capable of controlling the heating and cooling functions
so that the bath can be remotely operated at any temperature within the range of
the bath. To allow the interface to control the heating and the cooling, the front
panel controls are disabled by 1) switching the heater switch to LOW, and 2)
switching the refrigeration switch to OFF. Otherwise, the interface would not
be able to switch these functions off. The 7012 bath has four control functions
with the digital interface. These are heater power high/low, cooling on/off, ex-
pansion valve on/off, and back pressure valve on/off.
Heater Control
To control the heater with the digital interface the front panel heater switch
must be set to LOW (500 W). The heater function is controlled with the "F1"
command. Setting the "F1" parameter to 0 sets the heater to LOW (500 W) and
setting it to 1 sets the heater to HIGH (1000 W). Sending "F1" with no value
causes the controller to return a value showing what the heater setting is. When
the heater setting is changed a pop is heard as the heater relay opens or closes.
Cooling Control
To control the refrigeration power with the digital interface the front panel re-
frigeration switch must be off. The refrigeration power function is controlled
with the "F2" command. Setting the "F2" value to 0 turns the refrigeration off
and setting it to 1 turns it on. "F2" alone returns 0 or 1 showing the state of the
refrigeration power control.
The "F3" command controls the "high" and "low" cooling temperature range or
expansion valves. As discussed in Section 7.2 this valve adjusts the cooling
temperature which sets the cooling capacity. Setting "F3" to 1 opens the valve
(on or high) and 0 closes the valve (off or low). A command with no value re-
turns the current value. With the valve closed the cooling temperature is set
with the cooling temperature knob labeled "LOW". This should be adjusted for
approximately 9–14 psi if the bath is to be used as low as –10°C. The knob la-
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