Campbell Scientific CR23X Micrologger - Manual (Page 28)

CR23X MICROLOGGER OVERVIEW
OV-18
To make a thermocouple (TC) temperature
measurement, the temperature of the reference
junction (in this example, the panel
temperature) must be measured. The CR23X
takes the reference temperature, converts it to
the equivalent TC voltage relative to 0 o C, adds
the measured TC voltage, and converts the
sum to temperature through a polynomial fit to
the TC output curve (Section 13.4).
Instruction 14 directs the CR23X to make a
differential TC temperature measurement. The
first parameter in Instruction 14 is the number
of times to repeat the measurement. Enter 1,
because in this example there is only one
thermocouple. If there were more than 1 TC,
they could be wired to sequential channels, and
the number of thermocouples entered for
repetitions. The CR23X would automatically
advance through the channels sequentially and
measure all of the thermocouples.
Parameter 2 is the voltage range to use when
making the measurement. The output of a type
T thermocouple is approximately 40 microvolts
per degree C difference in temperature
between the two junctions. The
±
10 mV scale
will provide a range of +1000/40 = +250 o C (i.e.,
this scale will not overrange as long as the
measuring junction is within 250 o C of the panel
temperature). The resolution of the
±
10 mV
range is 0.33 µV or 0.008 o C because a
differential measurement is being made.
Parameter 3 is the analog input channel on
which to make the first, and in this case only,
measurement.
Parameter 4 is the code for the type of
thermocouple used. This information is located
on the Prompt Sheet, in the on-line help, or in
the description of Instruction 14 in Section 9.
The code for a type T (copper-constantan)
thermocouple is 1.
Parameter 5 is the Input Storage location in
which the reference temperature is stored.
Parameter 6 is the Input Storage location in
which to store the measurement (or the first
measurement; e.g., if there are 5 repetitions
and the first measurement is stored in location
3, the final measurement will be stored in
location 7). Parameters 7 and 8 are the
multiplier and offset. A multiplier of 1 and an
offset of 0 outputs the reading in degrees C. A
multiplier of 1.8 and an offset of 32 converts the
reading to degrees F.
In this example, the sensor is measured once a
minute, and the day, time, and average
temperature are output every hour. Once a day
the day, time, maximum and minimum
temperatures and the times they occur will be
output.
Final Storage data will be sent to Storage
Module. Remember, all on-line data output to a
peripheral device is accomplished with
Instruction 96 (Sections 4.1 and 12).
The first example described program entry one
keystroke at a time. This example does not
show the "A" key. Remember, "A" is used to
enter and/or advance (i.e., between each line in
the example below). This format is similar to
the format used in EDLOG.
It's a good idea to have both the manual and
the Prompt Sheet handy when going through
this example. Also look at the on-line help, key
, whenever “?” is displayed on the screen.
You can find the program instructions and
parameters on the Prompt Sheet and can read
their complete definitions in the manual.
To obtain daily output, the If Time instruction is
again used to set the Output Flag and is
followed by the Output Instructions to store time
and the daily maximum and minimum
temperatures and the time each occurs.
Any Program Control Instruction which is used
to set the Output Flag high will set it low if the
conditions are not met for setting it high.
Instruction 92 above sets the Output Flag high
every hour. The Output Instructions which
follow do not output every hour because they
are preceded by another Instruction 92 which
sets the Output Flag high at midnight (and sets
it low at any other time). This is a unique
feature of Flag 0. The Output Flag is
automatically set low at the start of each table
(Section 3.7).
OV5.3 EDITING AN EXISTING PROGRAM
When editing an existing program in the
CR23X, entering a new instruction inserts the
instruction; entering a new parameter replaces
the previous value.
To insert an instruction, enter the program table
and advance to the position where the
instruction is to be inserted (i.e., PXX in the
display) key in the instruction number, and then
key A. The new instruction will be inserted at
that point in the table, advance through and
enter the parameters. The instruction that was
at that point and all instructions following it will
be pushed down to follow the inserted
instruction.