Midi-Maestro and Maxi Maestro Drive
15
Maximum speed
RT resistor
Use the following equation to calculate the value of the
RT resistor:
RT Vm Ke
==××−−
200 5[( ) ]
Where:
Vm = Maximum speed of motor in
RPM ÷ 1000
Ke = Tachogenerator voltage constant
Resistor ratings:
Power: 0.25W
Tolerance: ±5%.
Note
If the calculated value of RT is zero, fit a link instead
of a resistor.
If the calculated value is negative, the tachogenerator
must be changed for one with a greater value of Ke in
order for the motor to reach the required speed.
Example 1
Max required speed = 3000
RPM
Tachogenerator output = 7V at 1000 RPM
1. Calculate:
RT k==××−−==200 3 7 5 3 2[( ) ] . ΩΩ
The value of the RT resistor may be between
2.7kΩ and 3.9kΩ.
2. Fit the resistor.
3. Apply speed reference signal of 2V to 10V to pins
9 and 10. (To generate this signal, use the
external controller or the reference voltage output
on pins 6 and 7.)
4. Measure the reference signal applied to pins 9
and 10 and calculate the tachogenerator output
value using the equation:
(())
Vdt =
RPM Vref Ke
10,000
××××
Where:
RPM = Maximum required speed
Vref = Measured reference signal
Ke = Tachogenerator voltage constant
Example 2
Max required speed = 3000
RPM
Vref = 5V
Ke = 10 (10V at 1000
RPM)
Vdt =
3000 5 10
10,000
15V
×× ××
==
Measure the tachogenerator output voltage with a
digital multimeter and adjust the maximum speed for
the multimeter to show the calculated value.
Calibration should be optimized using a speed
indicator.
Adjusting the nominal current
When the nominal current rating of the motor is less
than the nominal current of the Drive, it is possible to
reduce the maximum value of current produced by the
Drive by fitting a
RIN resistor.
Use the following equation to calculate the value
of the
RIN resistor:
RIN =
(10,000 I )
[(0.1925 I ) - (0.385 I )]
NOM
PEAK NOM
××
××××
Where:
I
NOM
= nominal desired current value
I
PEAK
= Drive peak current value
Note
I
PEAK
is a threshold level which is 2 × I
NOM
of the Drive.
When the value of the required nominal current is
reduced, the resulting I
PEAK
current may be more than
2 × I
NOM
before the I
2
t protection reduces the peak
current to the nominal value.
In this case, the peak current is supplied for less than
2 seconds. Added protection is required to stop the
I
PEAK
value increasing to more than 2 × I
NOM
. See
Adjusting peak current.
When I
NOM
is the theoretical nominal current, and the
denominator equals zero,
RIN should be open circuit.
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