Calculating display scale and offset values – Measurement Computing DBK70 User Manual
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B-4 Scale & Offset in Summary View
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Appendix B
Calculating Display Scale and Offset Values
Output Channel Icons are created for all channels supported in a DBK70 when the Read Current Settings
option on the Device menu is selected. One Output Channel Icon is created for each output channel in a
DBK70. Each Icon displays the channel number associated with the channel, the first 29 or so characters of
the Record Name and Comment fields of the DBK70 Database record used to configure the channel, and a
real time display of the value of the received data. The PC Display Scale and Offset, Record Name, and
Comments fields are described in an earlier section DBK70 Database Record Fields. A PC screen with
Output Channel Icons is shown later in the section Output Channel Icons.
This section describes the calculation of the PC Display Scale and Offset values used to scale received data
for display in an Output Channel Icon.
In absolute terms, the values that can be displayed in Output Channel Icons are integers that range from
-2
31
to +2
31
.
Example 1
Create a full range display in an Output Channel Icon (i.e., 0 to 10,000) equivalent to an RPM range of 0 to
10,000 RPM, where the data received from the vehicle data bus has a resolution of 0.25 RPM/bit
(i.e., V
H
= 10,000, V
L
= 0, D
H
= 10,000 RPM, D
L
= 0 RPM, and R = 0.25 RPM/bit):
If V
H
= 10,000, V
L
= 0, D
H
= 10,000 RPM, D
L
= 0 RPM, and R = 0.25 RPM/bit
PC Display Scale
= [(V
H
- V
L
) / (D
H
– D
L
)] * R
=
[(10,000
–
0)/
(10,000
–
0)]
*
0.25
=
[10,000
/
10,000]
*
0.25
=
1
*
0.25
=
0.25
PC Display Offset
= [(D
L
)/(R)] * PC Display Scale
= [ 0 / 0.25]
= 0
Example 2
Create a display with a range of -330 to +300 in an Output Channel Icon that is equivalent to a temperature
range of -300
°F to +300 °F, where the data received from the vehicle data bus has a resolution of
0.125
°F /bit (i.e., V
H
= 300, V
L
= -300, D
H
= +300
°F, D
L
= -300
°F, an R = 0.125 °F/bit
PC Display Scale
= [(V
H
- V
L
) / (D
H
– D
L
)] * R
= [(300 – (-300)) / (+300 – (-300))] * 0.125
=
[600/600]
*
0.125
=
1
*
0.125
=
0.125
PC Display Offset
= [(D
L
)/(R)] * PC Display Scale
=
[(-300)/(0.125)]
*
0.125
=
-2400
*
0.125
= -300