Display and Interface Design

Design Tutorial: Configural Graphics for Process Control 233
Low-Level Data
(process variables)
High-Level Properties
(process constraints)
T = time
V1 = setting for valve 1
V2 = setting for valve 2
V 3 = setting for valve 3
I 1 = flow rate through valve 1
I2 = flow rate through valve 2
O = flow rate through valve 3
R = volume of reservoir
K1 = I1 - V1 Relation between comman-
K 2 = I 2 - V 2 ded flow (V) and actual flow
K3 = O - V3 (I or O)
K 4 =
R = (I 1 + I 2 ) - O
Relation between reservoir
volume (R), mass in (I1 + I2),
and mass out (O)
G1 =
G 2 =
volume goal
output goal (demand)
K5 = R - G1 Relation between actual states
K 6 = O - G 2 (R, O) and goal states (G 1 , G 2 )
V1
I1
V2
I2
R
V 3
O
FIGURE 10.1
A simple work domain from process control. (Adapted with permission from Bennett, K. B.,
A. L. Nagy, and J. M. Flach. 1997. In Handbook of Human Factors and Ergonomics, ed. G. Salvendy,
Copyright 1997, New York: John Wiley & Sons. All rights reserved.)
Controlling even this simple process will depend on a consideration of
both high-level properties and low-level data. As the previous example indicates,
decisions about process goals (e.g., maintaining a sufficient level of
reservoir volume) generally require consideration of relationships between
variables (whether there is a net inflow, a net outflow, or mass is balanced),
as well as the values of the individual variables themselves (what the current
reservoir volume is).
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