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Old 04-29-2019, 09:34 PM   #1
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Default Yet another induction heater question...

Can someone explain to me the effects of induced voltages, say for instance, from 600kW induction heater? The reason I ask is because I’ve tried changing over our 120v inductive proximity switches over to a 24vdc shielded type. The prox switches are around 12-15’ away from the induction coils but I am still picking up a large enough induced voltage to set the proximity switch off. I am using a shielded cable and grounding it back to the control panel where the bonded control transformer and 24vdc power supply are located. I’ve exhausted everything I can think of to reduce this but to no avail.
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Old 04-29-2019, 10:17 PM   #2
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How are you measuring this induced voltage @ the switch? How much voltage is present? How much induced voltage is present @ the controller? Is there a clamping diode @ the controller? How well is the system grounded? Any current present on the ground? Why did you change out the functioning switches? What does the instalation manual say about induced voltages? Do you still have the old switches?
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Old 04-29-2019, 11:21 PM   #3
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How are you measuring this induced voltage @ the switch? How much voltage is present? How much induced voltage is present @ the controller? Is there a clamping diode @ the controller? How well is the system grounded? Any current present on the ground? Why did you change out the functioning switches? What does the instalation manual say about induced voltages? Do you still have the old switches?
I haven’t been able to measure anything, nor have I tried. I know it’s there because when the heater and loader are running the prox switch is blinking and closing randomly. With the heater and loader off, it’s like nothing ever happened. I reverted back today to the original 120VAC setup. The control box that is feeding the prox switches is sufficiently grounded and so is the loader but only at the I-line panels they’re fed out of no bonding to building steel. Ironically they’re both supplied from the same panel. No clamping diode of any sort. No current on ground. The prox’s are sensing the height of the ram on a drop hammer. Thus, there always getting damaged because they have exposed cable from the t’s to the switch themselves. Appx 8’. The cables are always getting damaged and frying the switch when they short or fault to ground. Would a capacitive switch help in an instance like this?
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Old 04-29-2019, 11:57 PM   #4
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We used 120 volt prox switches on our hammers. While we would change them from time to time, they really did not see too much damage from operation. They usually got damaged during a die change or something when someone raised the ram with something on it...

Now our proxs at the feeder were always getting changed because someone would always move the exit conveyor and the robot would smash them out when it tried to pick-up the ingot.

If you were going to go with DC I would look at your drains and I agree with the diodes too. I would also check to make sure your dies are not magnetized; the operators need to use more graphite or you need to put on a de-gaussing brush. We had to do this on one of our shot blast machines.

Cheers
John
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Old 04-29-2019, 11:59 PM   #5
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I haven’t been able to measure anything, nor have I tried. I know it’s there because when the heater and loader are running the prox switch is blinking and closing randomly. With the heater and loader off, it’s like nothing ever happened. I reverted back today to the original 120VAC setup. The control box that is feeding the prox switches is sufficiently grounded and so is the loader but only at the I-line panels they’re fed out of no bonding to building steel. Ironically they’re both supplied from the same panel. No clamping diode of any sort. No current on ground. The prox’s are sensing the height of the ram on a drop hammer. Thus, there always getting damaged because they have exposed cable from the t’s to the switch themselves. Appx 8’. The cables are always getting damaged and frying the switch when they short or fault to ground. Would a capacitive switch help in an instance like this?
I was thinking optical would be somewhat immune to noise. I suppose a good ol' mechanical limit sw. is out of the question due to harsh conditions. Capacitive may have coupling issues with induced signals. No shielding on the heaters? Could you replace the exposed cable with an armored type?
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Old 04-30-2019, 04:51 AM   #6
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Quote:
Originally Posted by joebanana View Post
Quote:
Originally Posted by TheDude_Abides View Post
I haven’t been able to measure anything, nor have I tried. I know it’s there because when the heater and loader are running the prox switch is blinking and closing randomly. With the heater and loader off, it’s like nothing ever happened. I reverted back today to the original 120VAC setup. The control box that is feeding the prox switches is sufficiently grounded and so is the loader but only at the I-line panels they’re fed out of no bonding to building steel. Ironically they’re both supplied from the same panel. No clamping diode of any sort. No current on ground. The prox’s are sensing the height of the ram on a drop hammer. Thus, there always getting damaged because they have exposed cable from the t’s to the switch themselves. Appx 8’. The cables are always getting damaged and frying the switch when they short or fault to ground. Would a capacitive switch help in an instance like this?
I was thinking optical would be somewhat immune to noise. I suppose a good ol' mechanical limit sw. is out of the question due to harsh conditions. Capacitive may have coupling issues with induced signals. No shielding on the heaters? Could you replace the exposed cable with an armored type?
No shielding that I know of. I definitely need to look into this. I may be able to sleeve 1/2” seal tight over the cables for added protection but I would need to look into how to support the prox switch end so the wait isn’t constantly tugging on the threaded connection
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Old 04-30-2019, 04:53 AM   #7
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We used 120 volt prox switches on our hammers. While we would change them from time to time, they really did not see too much damage from operation. They usually got damaged during a die change or something when someone raised the ram with something on it...

Now our proxs at the feeder were always getting changed because someone would always move the exit conveyor and the robot would smash them out when it tried to pick-up the ingot.

If you were going to go with DC I would look at your drains and I agree with the diodes too. I would also check to make sure your dies are not magnetized; the operators need to use more graphite or you need to put on a de-gaussing brush. We had to do this on one of our shot blast machines.

Cheers
John
The main problem that I see with the prox’s getting damaged is running the columns too loose. Lack of training and don’t give a damn. What kind of induction heaters did y’all use?
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