Specifications

10 CHAPTER 3. PERFORMANCE OF THE DACS
Aout
To Workspace1
Ain
To Workspace
Sine Wave3
Sine Wave2
PowerDaq PD2 MF
Analog Input
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
PD2_MF_Series1
PowerDaq PD2 AO
Analog Output
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
PD2_AO_Series1
[S9]
[S8]
[S7]
[S6]
[S5]
[S4]
[S3]
[S2]
[S0]
[S15]
[S14]
[S13]
[S12]
[S11]
[S10]
[S1]
j
i
h
g
f
e
d
c
p
o
n
m
l
k
a
b
[S9]
[S8]
[S7]
[S6]
[S5]
[S4]
[S9]
[S8]
[S7]
[S3]
[S6]
[S5]
[S4]
[S3]
[S2]
[S0]
[S15]
[S14]
[S13]
[S12]
[S2]
[S11]
[S10]
[S1]
[S0]
[S15]
[S14]
[S13]
[S12]
[S11]
[S10]
[S1]
1
Constant3
1
Constant2
Figure 3.2: Simulink model used in the experiments.
3.1 Performance
When a model is executed for the specified time period, it still takes about 4.5[s] to shut down the
Real-Time process. Furthermore the first few measurements are incorrect, due to initialization effects.
Depending on sample rate and the channellist, this can vary between 0 − 150 points.
When shooting for the highest possible performance for a certain set of channels, the sample rate
and Acquisition Delay need to be optimized. The sample rate should be chosen as high as possible.
The Acquisition Delay should be lowered until the read-out becomes rubbish.
A good procedure to check the performance of a certain set of channels is:
• Always check with a scope whether the model execution stays Real-Time.
• The desired set of channels and/or sample rate is known.
• When a maximal sample rate is desired.
– Configure the model in figure 3.2 according to the set of channels.
– Determine maximum sample rate, without loosing the Real-Time property (scope) or have
the PC not responding.
– Check if the read out of the channels is correct, adjust Acquisition Delay accordingly.
– If the Acquisition Delay is adjusted, determine the sample rate once more.
– It goes without saying that in the next step a sample rate smaller than the determined
maximum should be chosen.
• When the desired sample rate is known
– Configure the model in figure 3.2 according to the set of channels and the desired sample
rate.
– Write down the minimal value for the Acquisition Delay before the read-outs become rub-
bish.
– Increase the Acquisition Delay until the Real-Time property (scope) is lost, and write this
value down.
– Subtracting these two values gives the process-time available for controller calculation.
Knowing the sample rate, the percentage of the total time available for the controller can
be calculated.