Section 5
Page 5 - 16
HA243821
Issue 5 Mar 98
MODEL 346 INSTALLATION AND OPERATION MANUAL
5.6 DERIVED VARIABLES
5.6.1 INTRODUCTION
The derived variable feature provides basic and specialised maths functions. These functions combine channel
inputs, user-entered constants and pre-configured equations to derive variables which may be viewed, recorded
and/or used in other calculations.There are two classes of DV: basic and specialised. Because of processing
time allocations, only two specialised DVs can be used at any one time. The ‘basic’ functions are as follows:
Off
No Derived Variable (default state)
Add
A + B
Subtract
A - B
Divide
A B
Multiply
A X B
Lin. Slope
(A X B) + C
High Select
A > B = A
Low Select
A > B = B
High Peak
Highest value since reset
Low peak
Lowest value since reset
Average
Single point average
Polynomial
B + CA + DA
2
+ EA
3
The specialised functions are:
Log 10
B x log10A
Power 10
B x 10
A
Flow, Sq.Rt
Mass flow - Square Law
Flow, Linr.
Mass flow - Linear
F value
Sterilization F value (Fo)
RH
Relative humidity
ZrO
2
Sensor
Zirconia oxygen probe (Nernst oxygen equation)
Note...
To clarify the presentation of this section, the above formulae use letters A, B, C, etc. for derived variable
inputs. In the configuration menu, the Inputs are identified as ‘Input 1’, ‘Input 2’, ‘Input 3’ and so on, respec-
tively.
Derived variables (DV’s) take their inputs from channel inputs, other derived variables or constants and are
updated once every second. Each DV channel includes three registers for individual DVs. With two (or three) DV
channels, the six (or nine) DV registers are freely assignable to any DV channel.
DVs can be used like building blocks to construct formulae and equations as shown in the example below.
