H0 Sound Decoder MX640 Page 15
4. Additional notes to
Configuration Variables (CV’s)
Motor control frequency
and
EMF scanning rate:
Optimal Control, Automated Stops, Effects . . .
Two ways of programming speed curves:
Programmable speed curves can often optimize the driving characteristics of an engine. These
curves alter the relationship between the cab’s speed regulator settings and the engines speed
(that is between 14, 28 or 128 external speed steps of the cab and the 252 internal speed steps of
the decoder).
Which one of the two speed curves the decoder applies is determined by Bit 4 of Configuration Variable #29: “0"
assigns the first type - Three Step Programming, defined by just three CV’s; ”1" assigns the second type - Pro-
grammable Speed Table, defined by 28 individual CV’s.
Three step programming: by using the Configuration Variables #2 for Vstart, #5 for Vhigh and #6
for Vmid.
Vstart defines one internal speed step out of a total of 252 to the first speed step of the cab, Vhigh
to the highest speed step and Vmid to the center speed step of the cab. In this way a simple bent
acceleration curve can be achieved with an expanded lower speed range.
A slightly bent curve is active by default (CV #6 = 1), that is the center speed step is limited to 1/3 of
full speed.
Programmable speed table
:
with the help of the programmable speed table,
free programming
of
all
Configuration Variables
from #67 to 94 is possible. Each of the 28 external speed steps is as-
signed to one internal step (0 to 252). If 128 external speed steps are used, an interpolation algo-
rithm is used to calculate the steps in between.
NOTE
: The three step programming is in most cases entirely sufficient for good drivability; the relatively
complex procedure of defining a speed table is only recommended with the help of software like ADaPT
that graphically draws the speed curve and automatically sends the data to the decoder.
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28
0 9 18 27 36 45 54 63 72 81 90 99 108 117 1
26
Lin
ea
r c
ha
rac
te
risi
tc
-
Vs
ta
rt=
1,
Vh
igh
=2
52
, V
m
id=
12
7
Slightly bent
(default) characterisitc
Vmid = 1 (equals 85)
Vstart = 2
Vhigh = 1
(equals 252)
Center
150
160
170
180
190
200
210
220
230
240
250
In
te
rn
al
s
pe
e
d
s
te
p
External speed step
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28
0 9 18 27 36 45 54 63 72 81 90 99 108 117 1
26
Clipped linear speed curve
Vstart = 10, Vhigh = 165,
Vmid = 90
150
160
170
180
190
200
210
220
230
240
250
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28
0 9 18 27 36 45 54 63 72 81 90 99 108 117 1
26
Clipped and bent speed curve
Vstart = 15, Vhigh = 180, Vmid = 60
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28
0 9 18 27 36 45 54 63 72 81 90 99 108 117 1
26
Example of a freely
programmed speed
curve according to
the values entered
in to configuration
variables #67 - 94.
In case of
Faulhaber, Maxxon or similar
motors (Coreless):
Start with special
CV #9 = 22
and
CV #56 = 100
programming
! ! !
The
motor
is controlled by
pulse with modulation
that can take place at either low or high fre-
quency. This frequency is selected with
configuration variable #9
(NMRA conforming formula, see
CV table).
High frequency control:
The motor is controlled at 20kHz in default mode or whenever a value of
“0” is entered to CV #9, which can be raised to 40kHz with bit 5 in CV #112. The effect is compara-
ble to operating with DC voltage
and is likewise just as
noiseless
(no hum as with low frequency)
and easy on the motor (minimum thermal and mechanical stress). It is ideal for coreless motors
(recommended by Faulhaber!) and other high performance motors (most modern motors, including
LGB). It is not recommended however, for AC motors and some older motors.
When operating at high frequency, power to the motor is interrupted periodically in order to deter-
mine the current speed by measuring back-EMF (voltage generated by the motor). The more fre-
quently this interruption takes place, that is the higher the
EMF sampling frequency,
the better the
load compensation performs (see next page); but that also results in a certain loss of power. This
sampling frequency varies automatically in the default mode (CV #9 = 0) between 200Hz at low
speed and 50 Hz at maximum speed. CV #9 allows the adjustment of the sampling frequency as
well as the sampling time.
* It is recommended in most cases where an improvement is still required for
MAXXON, Faulhaber
or similar motors,
to select a lower sample frequency such as
CV #9 = 11, 12, 21, 31
etc after CV
#56 was programmed to 100; this will in any case reduce motor noise!
* for
older type motors
use rather the opposite, e.g.
CV #9 = 88.
Also see CV table and the following page!
Low frequency control:
Entering a value between 176 and 255 to CV #9 drives the motor between
30 and 150 Hz.
Most often used value is 208 for 80 Hz. This is rarely used today and is only suit-
able for AC motors with field coils.
The load compensation:
All Zimo decoders come equipped with
load compensation,
also known as BEMF to keep a
con-
stant speed,
regardless whether the engine is pulling a short or long train uphill, downhill or around
a tight radius (although the speed will not be held 100% constant, especially in the upper speed
range). This is accomplished by constantly comparing the desired value (speed regulator setting)
and the actual value at the motor, determined with the EMF method (EMF stands for Electro Motive
Force and is the force (power) produced by the motor when it is turned without power applied to it).
The
Reference Voltage
used for the BEMF algorithm can be defined by
CV #57
as either
absolute or relative (default).
Absolute Reference:
A voltage value is defined in CV #57 as a base line for the BEMF calculation. For
example: if 14V is selected (CV value: 140), the decoder then tries to send the exact fraction of the
voltage indicated by the speed regulator position to the motor, regardless of the voltage level at the
track. As a result the speed remains constant even if the track voltage fluctuates, provided the track
voltage (more precisely, the rectified and processed voltage inside the decoder, which is about 2V
lower) doesn’t fall below the absolute reference voltage.
