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Mystic meter 

Construction and operation

 The Mystic meter is a mechanical device constructed to dispense a specific quantity of tanning lotion during a specific time period (rate). The meter accomplishes this in a syringe fashion, first drawing in a charge of lotion into 3 separate cylinders, then dispensing this charge into the Mystic booth. The rate of delivery is set by the speed of cylinder movement. One way flow of the tanning lotion is created by the addition of two checkvalves in each of the 3 cylinders. The following pictorial shows the filling and then the dispensing of lotion in a single cylinder.

As indicated, the lotion cylinders are in a group of 3, one for each nozzle

All 4 cylinders within the meter are connected to a common follower plate. This follower plate is driven by a screw thread, which in turn drives the group cylinders to provide for filling or dispensing. The screw is driven by a 12 VDC motor through a reducing gearbox.

On early versions of meter, the inlet checkvalves where mounted on the cylinder fittings within the meter. Later models have moved them exterior of the meter, mounted inline with the pickup tubes.

Controls

The meter itself is run on 3 electrical wires, Common, Tan, and Rinse. Tan and Rinse are 12 VDC lines that provide full drive motor power. Power applied to the Tan line will drive the motor and screw so as to retract the cylinders. Power applied to the Rinse line will cause an extension of the cylinder rods. In both cases the PLC will drive a relay, which in turn will switch the 12 VDC power to drive the meter.

When a Rinse cycle is commenced by activating the Rinse pushbutton, the PLC will activate the rinse relay and hold it until the rinse cycle is complete. This cycle lasts approximately 1 minute. As the meter drive will have reached the end of its range prior to the cycle completing, the drive power must be interrupted to prevent an overdrive condition. This interruption is accomplished by the use of a reed relay mounted on one of the cylinders. When the reed relay senses the magnetic cylinder piston passing by, it will open, interrupting drive power.

As the magnetic ring passes under the reed relay, the relay will open, disconnecting power from the motor.

During a Tan cycle, the meter is driven for a specific time period, determined by the selected tan level. As a precautionary measure, a second reed relay is used to prevent the meter from overdriving in this direction.

To switch directions of the drive motor, a reversing relay resides within the meter. Power supplied on the Tan line will operate through the normally closed contacts of the relay. A 25 ohm potentiometer is installed in series with the motor, and is intended to provide some adjustment for motor speed control. Power supplied on the Rinse line will cause the relay to switch motor leads, thereby driving the motor in reverse direction.

The meter housing also holds the Rinse pushbutton. This is a separate circuit from the meter.

 

Check the following for additional information;

- meter schematics

- adjusting reed switches

Considerations

Life of the meter can be improved by several actions;

    - Cleanliness. Tanning fluid that may run down from the booth exhaust vent can pollute the electrical components of the meter. The wiring harness is particularly susceptible to fluid pollution. Keep the top of the meter wiped clean of fluids. Reset the exhaust filter to prevent/reduce spillage of fluids.

    - Rinse fluid circuit. On early booth models, the output of the rinse cylinder was connected to the water supply manifold immediately following the water solenoid valve. This resulted in high water pressure acting against the rinse cylinder which in turn causes the meter to misalign. The rinse output of the meter should be redirected to the overhead spiral nozzle. Mystic currently supplies this configuration on new booths.

    - Cylinder seals. Mystic supplied cylinders utilize an 'O ring' sealing element. This type of seal has a tendency to roll when the cylinder is used in this application. Once the seal has 'rolled', it's ability to seal is compromised. The result is that the seal allows a small amount of air to leak by on the fill cycle. This leaking air reduces the cylinders fluid capacity, and shows itself by causing the spray to fall behind on that particular nozzle. Purging the air will provide temporary relief. Dual lipped seals resist roll over and provide extended service. 

    - Checkvalves. These valves can leak if contaminated. The sealing tape used to seal the fittings can be particularly problematic if cleanliness during repair is not maintained. Generally, a warm washing of the valves followed by blowing out with compressed air will clear them of any contaminants. 

    - Cylinder rods within the meter will become dry during use. Particularly the rinse cylinder. Occasional lubircation will extend the life of the cylinders. This can be done by wiping the rods with a small amount of grease or oil.

Adjustment of Reed relays

As indicated in the construction and operation section, the reed relays prevent the meter from overdriving in either direction. To effectively adjust the relays, a 12 VDC power supply is required. Although it is possible to utilize the Mystic booth's power, a bench supply is the most practical. 

To begin with, review the meter schematics to become familiar with the circuit. Work on a non cluttered work surface. Observe all precautions associated with electrical exposures. The meter should be completely assembled. Best access is with the meter out of the cover.

Identify the three wires that drive the meter circuit, as they originate at the meter connector. As per the schematic and the actual meter, follow the Brown wire to its connection on one of the reed relays. This is Tan test point. Follow the Blue/w stripe wire to the connection on the other relay. This is the Rinse test point. Connect your 12 VDC common to the  meter common. The most practical location is found by following the Black/w stripe wire from connector to motor reversing relay. At the relay you will find a diode. Clip onto the common side of the diode. You are now able to drive the meter by applying + 12 VDC to either test point. The Tan test point will retract the meter while the Rinse test point will extend the meter.

Before applying power to the meter, understand that this process is about preventing overdrive conditions. Do not power the meter into an overdrive condition. Overdrive is evidenced by twisting of the follower plate and/or working of the drive motor  as one or more of the cylinders reaches the end of it's stroke.

Begin then by setting the Tan reed relay. The distance between the fixed and follower plate will be approximately 3/4" when the drive reaches the end. Apply power to the Tan test point and allow the meter to drive through retraction. Remove power if the meter travels beyond the 3/4" clearance. If this is the case, slide the reed relay toward the centre of the cylinder. If the meter drive stops prior to the 3/4" and no signs of overdrive are apparent, then slide the reed relay towards the rod end of the cylinder the approximate distance. Apply power to the Rinse test point to extend the cylinders approximately 1 ". Repeat the above procedure until the reed relay is cutting out the drive just prior to the cylinders reaching the end of their stroke. Secure the reed relay clamp being careful not to over tighten.

Setting the Rinse reed relay is done in similar fashion, reversing the test points. The follower plate will extend to approximately 5 1/2" as it approaches the end of the meter stroke.

Suspect reed relays can be tested by removing from circuit, applying an ohm meter across the relay, then sliding the relay over the cylinder with magnetic piston. The relay is normally closed and will open in close proximity to a magnetic field.

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