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Discuss Sequential reversing starter for metal detector conveyor in the Industrial Electrician Talk area at ElectriciansForums.net

sysrq

Regular EF Member
Can't seem to find any standard circuit diagrams for sequential reversing starter. The metal detector conveyor has manual mode and automatic reversal mode. Need to prevent the conveyor from going backwards during false signals or anything else while the conveyor is standstill. It should reverse only after it has been going forwards, and it should be made possible to reverse it in manual reversal mode after conveyor has stopped after detection of metal.
Might need to post a current wiring diagram which is made around Lock Metalcheck 9 metal detector with NO, NC contacts.
It should be fairly easy but the brain seems like it doesn't want to needlessly overstrain itself lol.
 
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mickfred

Regular EF Member
I take it that belts runs forward metal detector dents signal back to board , the board revises the belt a predetermined time and a person manually removes metal and press a button to set a signal back to the board and the belt goes forward
 

sysrq

Regular EF Member
Well, the first thing that needs to be sorted out is intermittent stopping of a forward contactor due to change-over between COM and NO/NC contacts on splice nullifier timer relay. It happens even when the time delay is set on longer than 3 seconds which is long enough to override the rejection time.
Tried to disconnect the timer input signal coming from metal detector head itself but that stops it as soon as inductive proximity senor sees the splice, so will have to temporary connect some pull-down resistor between the signal and ground. One is provided with the timer unit itself, with one end floating. Some of the identical ones doesn't have any resistor at all. Nothing has been staid about it in the manual. Another option might be to utilize the conveyor speed signal input if possible.
 

sysrq

Regular EF Member
Probably will have to add some capacitor for short duration ride-through since it's a 24V DC contactor. Since there are mechanical interlocks in place there might not be any negative effect on reversing starter due to prolonged dropout times. Another option would be to use timer with solid state relay.
 

Carl S

Regular EF Member
Is this for a food processing plant? If it is, you are skating thin ice if you modify the metal detector without consulting the manufactures.
 

netblindpaul

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This must all be CE marked, if it’s not working safely then the law has been broken. Be careful with what you do.
 

sysrq

Regular EF Member
According to some other sources only LC1D09BD has integrated back EMF suppression, hence the confusion.
 

darkwood

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What do you call 'false signals or anything else' - it seems an odd design set-up from the off and I assume it cannot be accidentally operated triggered as that would bring into question the safety of the design. There are simpler and more practical ways of doing this especially with the popularity of VSD's which has brought down the costs to levels which are very competitive to fitting reversing contactors and overloads to boot.

You need to address what is causing the false alarms here failure to do so may let metal through and I am guessing that could be a costly issue given the need for the detector in the first place.

So what is the machine doing, is it feeding fibre into carding rolls or anything else in the textile related industry?
 

sysrq

Regular EF Member
I have been told using VSD in close proximity with metal detector is not advisable, due to interference. Don't know if multi-frequency ones are more immune. 300kHz operarating frequency might too close to VSD PWM range.
The main culprit in this case is old and dirty conveyor belt with rust marks on it.
It's not a textile, but a second hand plastic scrap.
 

darkwood

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I have been told using VSD in close proximity with metal detector is not advisable, due to interference. Don't know if multi-frequency ones are more immune. 300kHz operarating frequency might too close to VSD PWM range.
The main culprit in this case is old and dirty conveyor belt with rust marks on it.
It's not a textile, but a second hand plastic scrap.
Not sure where you heard that from but correct shielding and segregation are normally good enough although you may still get issues these can be rectified using galvanic isolation signal conditioners.
 

netblindpaul

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It's a private project built form scratch and there isn't any edible matter in vicinity.
...
If it's used for anything else other than "personal"/"private"/"DIY" use, in other words if it is used in a business of ANY kind, it must be CE marked and compliant with the law.
This situation of companies building equipment for their own use is specifically included in the Regulations, to prevent employees being put in danger from equipment that their employer decided to throw together.
If you are not using it in a business of any kind then great, but, if you are then you are subjected to the whole raft of requirements, as would any other company placing a machine on the market.
 

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