Design notes for heater control on Genosensor model "Delta".

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Revision History:

5:57 PM 10/19/1999 Initial release, DKW.
10:24 AM 10/20/1999 Updated links DKW.
11:54 AM 12/03/1999 Specific parameters for ST-5000
11:30 AM 05/11/2000 Changed ST-5000 averaging from 
16 points to 4 points/second. Otherwise, have a 4 second lag
due to 4 sample/sec moving average rate. DEC
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Filter holder temperature is sensed by an Exergen Corp. model number
IRt/c.03-J-140 infrared "thermocouple". It produces a signal output 
that matches the J type thermocouple curve at approximately 20C. For
temperatures above that point the IR sensor has a higher output voltage
than a true thermocouple. In addition to being nonlinear with respect to 
a thermocouple, its output is dependent on the emissivity of the material 
within its field of view. These factors need to be accounted for in
applying corrections to the indicated temperature from the IR sensor.

In addition to the error sources specific to the IR sensor, there are 
issues related to thermocouples in general. Cold junction compensation 
and voltage gain of ~400 will be needed as well. Rather than reinvent 
the wheel, I have chosen to purchase a signal conditioning module 
recommended by Exergen. It is the Applied Technology Concepts model ST5000.
See: http://www.atconcepts.com/new.htm and ST-5000.pdf for info.
The ST5000 module is "smart" in that it can both linearize the IR 
output, and apply a correction for the emissivity of the material.
The module generates a 4-20mA signal at its output, and draws power 
from the loop supply. This current mode output will be converted to a
400mV to 2000mV signal across a 100 ohm resistor. The voltage thus generated
can be sampled by an A/D input on the DM5210 multifunction card. The A/D is 
configured for 10 volt single-ended input, and having 12bits resolution
will give us ~655 counts of resolution over our 4-20mA span. The ST5000 
module can be configured to convert any desired temperature range of 
interest to the full 4-20mA span. If, for example, we select 20C to 100C
as our range, we will have 0.12 degree C resolution. 

As of this writing (11:58 AM 12/03/1999), the ST-5000 has been configured for
an Exergen model IRt/c.03-J-140 sensor, the emissivity factor has been set  
to .93 as recommended for a painted surface, and the output has been scaled
for the 20C-100C range.  In addition to being sabctored in the flash memory onboard 
the ST-5000, the configuration parameters are in the file "GenoDelta01.st5" for 
cloning of additional ST-5000 units. 


The Windows application used to configure the ST-5000, "TRANScon" has been
archived under the software revision control system for safekeeping.
See D. Cline for retrieval if it is necessary to re-configure the unit.
[DEC 11:41 AM 05/11/2000]. You may experience difficulty installing the 
TRANScon software from floppy disk.  Try copying the software from floppy to 
your hard disk and installing from hard disk.  Otherwise, contact the company for a new 
copy of their configuration software. See  http://www.atconcepts.com/new.htm .

Control of the power to the heater will be binary. A single output bit 
has been assigned to an FET power switch. The temperature control algorithm 
will execute as a task in the main PC/104 CPU.  See software document 
http:\\mww.mbari.org\genosensor\software\doc\tempcontrol.txt for details on the 
software temperature control algorithm.

See "Geno104Addr.txt" for specific port assignments.


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