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SHIM
POWER SUPPLIES - MXA SERIES
OUTPUT
RANGE AND DUTY CYCLE
The
MXA shim power supplies are compatible with the resistive shim drums designed for the MR
scanners. The resistance and
inductance for the shims should not exceed 5 ohm and 20 mH. Total
output is 20 amps cumulative for the power system.
The current limit at the load is related to the load resistance. The shim supply is rated for continuous duty cycle.
|
Range |
+/-
5 amp full scale |
|
Voltage |
+/-25
volts maximum |
|
Full
Power Bandwidth |
DC
to 50 kHz |
|
Loop
gain |
60dB |
|
Total
output is 12 A
cumulative and will not exceed +/- 12 A |
ACCURACY
AND STABILITY
|
Resolution |
16
bits (+/- 15 bit full scale) |
|
Monotonicity |
13
bits |
|
DC
Offset trim |
+/-
1% full scale (internal) |
|
Zero
Drift |
Not
more than 30 ppm per day |
|
Gain |
+/-
1% |
|
Gain
drift |
± 50 ppm per 24 hours |
|
Noise |
< 50 ppm for
10Hz to 50 KHz
15 ppm
p-p 0.1 HZ to 10 Hz |
LOAD
MATCHING
|
Load
resistance |
2.5-6
ohm (including cable)
NOTE: higher resistance is allowed but will limit the maximum
current ratings |
|
Load
inductance |
0
to 20 mH (including cable) |
|
Load
capacitance |
0
to 100 nF (load to load capacitance and detailed distribution is
critical - consult factory) |
|
Rise
time (10-90%) |
100
µS (small signal) |
|
Rise
time (10-90%) |
1000
µS (full scale) |
|
Settling
Time |
± 15 ppm of full scale within 2000 mS |
DYNAMIC
OPERATION
|
Speed of the
digital input |
Baud
rate of the RS-232 and the computer speed
In
most cases the baud rate (normally 19200) is an overwhelming limitation
|
|
Speed of the
digital-to-analog conversion |
Conversion
rate of the DAC’s used in the system is 2 microseconds |
|
Gain of the
amplifier |
Closed
loop gain of the system power amplifier measured into resistive load
(test conditions) is in excess of 50 kHz
In
most cases the response is limited by the power supply voltage
|
|
Impedance of the
load
|
Limited
only by the power supply rail voltage |
|
Power supply
voltage |
Maximum
voltage swing of the power amplifier is +/- 24 volts |
|
Limitations
of the
response bandwidth |
Power
supply voltage - the maximum voltage swing of the power amplifier is +/-
24 volts.
Impedance
of the load
Gain
of the amplifier |
STATIC
OPERATION
The
primary characteristic of the MXA limiting the static operation is the
precision and stability of the output.
The design and parts selection for both the
digital-to-analog conversion and the analog feedback circuitry present
very high performance capabilities. The
limitations are:
|
Resolution |
16
bits (+/- 15 bit full scale) |
|
Monotonicity |
13
bits |
|
DC
Offset trim |
+/-
1% full scale (internal) |
|
Zero
Drift |
Not
more than 30 ppm per day |
|
Gain |
+/-
1% |
|
Gain
drift |
± 50 ppm per 24 hours |
|
Noise |
<
50 ppm for 10Hz to 50 KHz
15 ppm p-p 0.1 HZ to 10 Hz |
|
Shunt
precision |
1% |
|
Shunt
TCR (temperature coefficient of resistivity) |
10
ppm/deg.C |
|
Shunt
Power Dissipation |
3.4
deg C/W |
SAFETY
AND REGULATORY ASPECTS
Magnetic
field environment safety
The
MXA system contains significant mass of ferromagnetic components, in
particular in the power supply section.
Those include case materials (steel) and transformers.
Care has been taken to use non-ferromagnetic fasteners wherever
possible, however, the manufacturer cannot assure that all removable
components of the system will not be compatible with high magnetic
fields.
The
MXA shim power supplies are certified to UL-2601, IEC-601, or CSA-601.
ENCLOSURE
AND WEIGHT
|
Packaging |
Cabinet Mounting - The shim
supply can be rack mounted into a standard 19" sub-rack enclosure,
3U or 6U high and 27.5" (700 mm) deep. |
|
Weight |
Total weight:
45 kG to 70 kG,, depending on the number of channels |
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