2-4
Functional Description
Onboard memory includes ROM, Static RAM, and Dual-Port Static
RAM. ROM contains the DAS-TC/B control program, which directs the
activities of the microprocessor and the thermocouple look-up tables.
Static RAM serves as the CPU “scratch pad,” providing temporary
storage for measurement results and calibration coefficients. The
dual-port RAM is the buffer for communications and data flow to/from
the computer.
Operational Flow
Configuration data for the DAS-TC/B board and channels is contained in
a configuration file. The configuration file is generated through
DriverLINX.
During DAS-TC/B initialization, the CPU downloads configuration infor-
mation from the computer hard drive to the DAS-TC/B board memory.
The CPU then sets up the DAS-TC/B board and channel parameters to the
specified values. Following parameter setup, the CPU performs a calibra-
tion and stores the gain and offset coefficients in board memory. Next, the
board reads and stores the CJC sensor value.
When the PC initiates a channel scan, the DAS-TC/B scans the channels
in the order specified by the PC. Channels designated for thermocouple
input use parameter values from the configuration file. Channels desig-
nated for voltage input also use parameter values from the configuration
file, unless you overwrite these values.
Channel readings proceed at less than the rate specified by the value for
Normal Mode Rejection Frequency in the configuration file. The reading
for each channel requires a count of the frequency output of the V/F con-
verter. The CPU compensates for calibration errors in these readings. For
channels configured as thermocouple inputs, the CPU also adjusts for
CJC and converts the readings to temperature measurements. For chan-
nels configured as voltage inputs, the CPU converts the readings to volts.
