Fluke NetDAQ 2640A Manual de usuario descargar pdf (Pagina 251)

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

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Fluke NetDAQ 2640A Manual de usuario Pagina 251