In February 2007 the Motor 4 of the altitude axis was found in short circuit. The symptom was, when getting the command "online" the telescope make a short run away until the online condition is reached. In the Altitude Axis plot you can see that the plot is not centered in a zero volt balanced condition. At the beginning the motor was in short circuit, and afterwards due to the extensive test made in order to readjust the servo to work with three motors only, the motor 4 go to open circuit.
In order to continue operations with three motors, the amplifier number 4 was connected to a resistive load of 4 ohms. In the mean time, a technical time was asked for February 10 - 12 and also, a spare motor was prepared.
Test for the spare Motor before the change.
1. Electrical Isolation
2. Torque Conditions
3. Oil Tight
4. Check with a ohmmeter that the motor is really the one that you have to
change!!
Mechanical Task for the motor change over
1. As the Motor 4 is mounted in the B side EMMI Instrument has to be move
out fromthe adapter. After this the motor cover is totally exposed.
2. Disconnect all cables and hoses, and put it inside the access holes, in
such a way that they do not oppose to the motor extraction. (See Motor
6 photograph). Take care to have a way to recover it after.
3. A special table to extract
the motor has to be installed in the motor area. All the screw that are
tighten the motor have to be taken out. (See Motor3,
Motor4, Motor5,
Motor 11, photographs)
4. Remenber that you can use the twin motor to check mechanical or electrical
detais. In this case you can see Motor 2 from the Motor7
photograph.
5. In the process of taking out the Motor you have to use a Power Supply over
35V and 10 amps, in order to release the motor brake. (See Motor28
photograph)
6. The main mechanical problem to take out the Motor (when the motor doesn´t
have a special screw to put away a fixation Ring), is to take out a fixation
ring with a special tool to take out it. (See Motor40
and Motor41 photographs)
7. Now with the special table you can take away the motor. ((See Motor12,
Motor13, Motor14,
Motor16, photographs)
8. Clean all the area.
9. Now you can install the new motor in the telescope. Remember that you will
need the Power supply to release the motor break. (See Motor18,
Motor19, Motor20,
Motor21, Motor22,
Motor23, Motor24,
Motor25, photograph)
10. Once the motor is in position, is will be necessary to adjust the paralelism
of the gear tooth. To do that, all the motor have to be rotated over it axis.
The way to do that is using the crane. (See photographs, Motor26,
29, 30,
31, 32,
33, 34,
35, 36,
37, 38,
42 .)
Electronical Task after the motor change.
Power Amplifier test
1. Install a Signal Generator with a dual channel oscilloscope in the area
of the amplifier
2. Put a high power 4 ohm load at the output of the Power amplifier under
test
3. Put the output of the signal generator in the input of the amplifier with
the special connector from the NTT Power Amplifier test bench.
4. With BNC T connector at the output of the Signal Generator connect the
second cable to the input A of the Dual Channel Oscilloscope.
5. Connect the channel B of de Dual Channel Oscilloscope to the output of
the amplifier. Use the Power Amplifier output connector of the NTT Power Amplifier
test bench
6. Connect a power supply of 60 volts and 15 amps minimum to the Power Amplifier
output connector of the NTT Power Amplifier test bench. Set it first to zero
volt and 10 amps limit current. No matter with the polarity because a bridge
rectifier is at the Power amplifier.
7. Set the Signal Generator to give a sinusoidal wave with a frequency of
100mHz, zero offset, and with an amplitude of 10mv.
8. Test the amplifier by increasing alternating the amplitude of the signal
generator and after the voltage of the Amplifier power supply. At the end
you can have all the power supply voltage and you can see a clipping of the
output wave at the level of the applying power supply voltage. Remember that
the maximum voltage applied to the Power Amplifier is 120Vdc. You have to
see a perfect sine wave. (Some distortion near the zero crossing is acceptable.
Motor test at Telescope.
1. At the motor site, connect the motor to an external Power Supply (40Vdc
and 10 amps). Use a special box with the proper LEMO connector that it is
the NTT Laboratory cabinet.
2. Connect a bridge between pin 15 and 16 of the strip terminal 6 (ST6) at
the power rack corresponding to the axis under test, Altitude in this case.
This is to release all the motors brakes of the axis.
3. With the motor power supply increase the voltage up to see some movement
of the telescope. This normally happens at a current of 5.5 amps and 25Vdc
in altitude, when the friction is overcome
Step Response of a Motor
1. Install a Signal Generator with a dual channel oscilloscope in the area
of the amplifier
2. Connect a T BNC connector to the output of the Signal Generator
3 . Disconnect the BNC velocity PI input at the upper Altitude rear panel
rack.
4 . Connect one end of the T BNC of the output of the signal generator to
the BNC velocity PI input at the upper Altitude rear panel rack.
5 . Put the other output of the Signal Generator in to the input A of the
Dual Channel Oscilloscope. .
6 . Connect the channel B of de Dual Channel Oscilloscope to the output of
the tacho BNC signal at the Altitude upper front panel rack.
7 . In the system set the AltServer in online status (By safety reason it
will be good to set previously, the telescope Altitude at 50 Degrees aprox,
because the telescope will start in oscillation and a drift can be possible).
8 . Set the Signal Generator to give a square wave with a frequency of 100mHz.
Set the offset at a level that the minimun signal voltage is over zero in
10 mv approx.Set the amplitude in 50mv.
9 . With this test you will have a signal like the ones shown in photographs
1, 2,
3, 4.
The time to have a stable response is 300 msec approx.
10. Altitude Data from Resistor values at Altitude PI
Board Potentiometer.
Altitude Motor System Response
1. 1. Install a Signal Generator with a dual channel oscilloscope in the
area of the amplifier
2. Connect all the amplifiers connectors
3 . Put the output of the signal generator into the input of the PID at the
Altitude Upper Rear Panel Rack.
4 . With BNC T connecto at the output of the Signal Generator connect the
second cable to the input A of the Dual Channel Oscilloscope.
5 . Connect the channel B of de Dual Channel Oscilloscope to the output of
the tacho signal at the Altitude Upper Front Panel Rack.
6 . Connect a bridge between pin 15 and 16 of the strip terminal 6 (ST6).
This is to release all the motors brakes of the axis.
7 . Set the Signal Generator to give a sine wave with a frequency of 100mHz.
Set the offset to zero. Set the amplitude in 50mv (After you can change up
to 2 volts.)
8 . With this test you will have a signal like the ones shown in photograph
5. The time to have a stable response
is 300 msec approx.
9. Now the telescope have a motion back and forward. The amplitude depends
of the input from the Signal Generator. In the telescope area you have to
check noises and mechanical behavior.
This is the end of the hardware check.
Agustin Macchino. 12FEB2007
