Electronics 500-P - Manual (Page 3)

IM0053A Page 3 of 10
1. General
The model 500 MagnaValve is a magnetic valve capable of regulating the flow of
steel shot in the range of 0-1200 pounds/minute. The magnetic engine has no moving
parts but relies on a strong magnetic field to hold or release the shot.
The built-in sensor measures shot density as it is discharged from the bottom of
the valve. This measurement is converted to a 0-5 V dc signal for process control.
2. Principle of Operation - Engine
The vertical passage through the valve is the flow path for the shot, sized to flow
more than its rated capacity. The upper portion of the valve is the magnetic engine.
Located on either side of the bore are two pole pieces of a very powerful permanent
magnet. The magnetic field is strong enough to prevent the flow of ferrous media (steel
shot).
An electromagnetic coil is mounted on each side of the two pole pieces. When
these coils are energized, the permanent magnet field is (perfectly) cancelled and shot
will freely flow through the valve. The valve, therefore, acts as a "normally" off flow
valve for ferrous media.
To control or regulate the shot flow rate, the coils are energized in a time
proportioning manner -- sometimes called duty cycle. If the coils are energized at 50%
duty cycle, then the flow rate will be 50% of the valve capacity. The repetition rate is
fixed at 8 Hertz (125 msec period). A red LED signals that power is applied to the coil.
If the LED is off, then there should be no shot flow. If the Led is on (constantly), then
full shot flow rate will occur. If the LED is blinking, then a controlled or regulated
intermediate shot flow rate will occur.
The dc current for the coil necessary to perfectly cancel the permanent magnet is
established by the valve driver module. An adjustment trim pot on the module is factory
set to the dc current (amps) indicated on the valve driver product label. NOTE: this
value is only valid at 100% duty cycle when the red LED is constantly on.
3. Principle of Operation - Sensor
The lower portion of the valve is an inductive metal sensor used to detect the
amount of ferrous steel shot passing through the engine. The sensor is an oscillator
circuit operating at a base frequency of 11,400 Hertz. The oscillator frequency will
decrease with increasing flow rate (about 1000 Hertz for full range). This signal is then
converted to a 0-5 V dc output signal.
For high accuracy applications the built-in linearity compensator may be used.
Additional information is shown later in this manual for its adjustments. The
compensator will add (or subtract) offsets at 10% increments.
4. Mechanical Installation
The MagnaValve must be mounted in a vertical position, paying attention to the
"flow arrow" decal on the outer housing. Mounting the valve at more than 10 from
vertical will promote rapid wear of the internal flow path and may also restrict the
maximum flow rate. Mounting the valve in the non-vertical position is not recommended.