NetDAQ Users Manual

E-1
Appendix E
Computed Channel Equations
Introduction E-1.
An equation is converted into a stored binary format which is sent to the
instrument where the calculations are performed during the processing of each
scan. Constants are passed to the instrument as single precision (4 byte) floating
point numbers which have a maximum magnitude of 3.402823E38. Calculations
and intermediate values in the instrument use double precision (8 bytes) in order
to preserve resolution. The resulting computed channel value is a single precision
floating point number. When the result is >9999.9E+6 or<-9999.9E+6, NetDAQ
Logger displays +OL or -OL for that channel, and changes the channel value to
+1.0E+9 or -1.0E+9, according to the sign.
The instrument traps math errors such as divide by zero and log (0) and returns a
non-numeric result which the logger reports as +OL. If a the value of a reference
channel is non-numeric (indicating an open thermocouple or overload), that value
will be returned for the computed channel.
Computed channel equations must observe the following syntax:
• White space is allowed, but not required, between symbols.
• White space and parentheses do contribute to the 100-character limit for the
text string, but do not contribute to the size of the stored binary equation (all
stored binary equations for an instrument cannot exceed 1000 bytes).
• Alphabetic characters may be in upper or lower case.
The symbols used in the syntax definition have the following meanings:
<> enclose an element which needs further definition
{} enclose elements that may be present zero or more times
[] enclose elements that may be present zero or one time
| separates alternative elements