Proximity Switch

General - Installation / Wiring - Troubleshooting

The job of the primary PID control loop is to keep the various mechanisms running at the proper production speed. However, just running at the proper production speed is not enough. For example, on a glass machine, the blanks should be in the “load” position as the gob leaves the deflector. It would be a catastrophe if the machine were in the middle of transfer when the gob was leaving the deflector. The relative position (phase) of the mechanisms can either be detected manually or automatically. Automatic detection requires two proximity switches. One proximity switch is used to detect the position of the lead motor and the second proximity switch is used to detect the position of the following motor.

All drives using independent motors require differential adjustments when the motors are first started. This phasing could be automatic or manual depending on the drive.

If the drive system consists of a single AC source such as the Synchrotie sender on the feeder PIV or its modern day counterpart of one large Variable Frequency Drive (VFD) and multiple synchronous slave motors, then phasing is no longer a problem once the initial alignment has been done.

On the other hand, if multiple smaller VFDs are used the mechanisms will eventually drift out of position. Even driving synchronous motors will not help as the root cause of the problem is with the tolerance of the crystals used for the microprocessors at the heart of the VFD electronics. Typical tolerances of crystals are on the order of 100 parts per million with some high accuracy crystals available with 20 parts per million variation. It has been measured that a feeder and gob distributor can move .070 seconds out of position and still “load” even at 170 cuts per minute. This may not seem like much, but if the 2 VFDs used to run the feeder and gob distributor motors had crystals that were different by 20 parts per million, it would only take (1,000,000 / 20) * .070 seconds = 58 minutes to exceed the limit. Even if the crystals driving the electronics were closer in tolerance, production would still go down within a few hours without some type of automatic intervention.

A multiple VFD drive requires proximity switches and automatic differential adjustment.

When choosing a proximity switch, keep in mind that some brands are sensitive to common mode noise and require grounding at the mechanism. This practice can lead to ground loops and is not recommended. Also keep in mind that the switches are mounted in hot locations. Experience has shown that a proximity switch rated for operation at 100 deg. C. will perform satisfactorily.

Although many proximity switches will work satisfactorily, we have used Turck model # Bi5-S18-AN7X/S100 for better than 20 years. It is a proven proximity switch near IS machines. To find a local source for your area click on the following link: www.turck-usa.com/Support/International_Sales_Channel/

Installation / Wiring

If unfamiliar with mounting and/or using proximity switches, consult the manufacturer’s web pages for the proximity switch that you are using.

Synphase provides an optically isolated input for each of the 3 proximity switch connections per control card. A floating 24 volt DC power supply is also provided for your convenience in wiring the proximity switch.
  • First Generation Synphase cards
Originally, Synphase cards were designed to only use “sinking” proximity switches. Connecting only the signal lead from the proximity switch to the field wiring connector permitted the use of 3-terminal connectors. The disadvantage was the loss of termination flexibility created by the internal circuit traces on the printed wiring board. The circuit diagram for first generation Synphase cards’ proximity connection is shown in Fig.1.

Figure 1 - Note that the isolation LED is internally connected to the +24 VDC and not available for external connections.

  • Second Generation Synphase cards

The double pole double throw switches mounted near the proximity switch field terminations can identify these 2nd generation cards. This switch changed the connections to both sides of the isolation LED. With this arrangement, either “sinking” or “sourcing” proximity switches could be used and the field termination connector remained at 3 poles. The circuit diagram for 2nd generation Synphase cards’ proximity connection is shown in Fig.2.

Figure 2 - Change switch contacts to lower position when using a “sourcing” proximity switch.

  • Third Generation Synphase cards

Although the +24 volt power supply on the Synphase control card is isolated, other equipment manufacturers were hesitant to connect their optically isolated outputs to the Synphase optically isolated inputs. These other suppliers insisted on using a third level of optical isolation.

The field connector for each of the 3 proximity switch connections was increased from 3 to 6 poles allowing both sides of the optical isolation LED to be completely independent of the rest of the Synphase board. With this modification, it is possible to use either “sinking” or “sourcing” proximity switches deriving their power from the Synphase board. It is also possible to make connections to other “foreign” equipment that provides its own power to drive the LED.



This picture shows the wiring for a “sinking” proximity switch on a 3rd generation Synphase card. The outer 2 wires are connected to the internal isolated power supply and are used to provide operating power to the proximity switch. The inner wire on the right is the switched output from the “sinking” proximity switch and the jumper wire is used to connect the positive side of the LED to the +24. Refer to Fig. 3 for the circuit diagram of this connection. Note that this exactly duplicates the circuit in figure 1 except that the connection between the +24 supply and the + side of the isolation LED is off board instead of internal.

Figure 3 - Showing the connections for the 3 wires from a “sinking” proximity switch and the jumper to the positive side of the LED.

When a “sourcing” proximity switch is used, the 3rd wire (signal) is active +24 volts. In this situation, a jumper is required between the negative LED input and the supply GND as shown in figure 4.

Figure 4 - Showing the connections for the 3 wires from a “sourcing” proximity switch and the jumper to the negative side of the LED.

Sometimes it is necessary for 2 systems to require timing signals from the same mechanism. An example might be Synphase running a feeder and electronic timing on the same IS machine. Here each system requires a synchronizing signal from the feeder shear cam.

At the option of the service personal overseeing the installation and start-up, it is possible for Synphase to accept a completely isolated signal from the “other” proximity switch powered by “others” instead of mounting a duplicate proximity switch on the mechanism. Refer to figure 5 for this connection.

Figure 5 - Showing Synphase wired for a total isolation input.

Troubleshooting

When initially installing, or when checking for functioning use the 2 LEDs provided.

The Turck switch referenced above will activate when a metal target is within 5 mm (.200 inch) of its face. When it does activate, its integral LED will turn on. Use this LED to confirm the 2 power supply wires from the Synphase card are functioning properly and the switch is activating when the target or flag travels in front of the proximity switch. If the proximity switch is powered and a screwdriver is placed against the head of the switch, the proximity LED will illuminate. If it does not, either the power is missing or the switch is bad.

Once it has been confirmed that the proximity switch is operating properly, observe the switch as the target passes in front of it. If there is no flash of illumination from the LED, the gap is too large.

The Synphase card has an LED in series with the opto-isolator input chip for the proximity switch. When the proximity switch is active, the chip LED on the Synphase card will be illuminated. Note the illuminated yellow LED in the above picture of a third generation card. You can use this LED to check for proper connection of the 3rd wire from the switch (the signal).

If there is any doubt about the field wiring, the proximity switch in question can be connected directly to the side of the Synphase card once the field wires have been removed. A screwdriver or other tool waved in front of the switch’s sensing face should activate both LEDs.

Erratic Signal:
Looseness (and movement) of the target will cause variations in cycle times. Backlash or run out in the mechanical connections between the motor shaft and the proximity switch may also cause variations in cycle times. Use the diagnostic page of the Synphase operator’s interface to identify timing jitter.

Right click and save target as:
Proximity.pdf
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