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Please advise a device to change a pulse to on/off signal

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h_h

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A EC Fan output a signal 3 pulses per revolution (Isink max = 10 mA), please advise a device to change this signal to on/off signal so that output ON when the Fan is running and OFF when the Fan is not running.
Let me know a specific model would be greatly appreciated because I am green for electronic, thanks!
 

crutschow

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A missing pulse detector would work for that purpose.
Here's an article on those.
 

alec_t

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You could also look up 'retriggerable monostable'.
Welcome to ETO!
 

h_h

New Member
Thanks crutschow and alec_t, but any relay can do this (close when there has pulse, open when there has no pulse)? the pulse is about 47V, 3 pulses per revolution (Isink max = 10 mA), thanks!
 

ci139

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Last edited:

alec_t

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any relay can do this (close when there has pulse, open when there has no pulse)?
Depends on the interval between pulses and the pull-in/drop-out times of the relay. You would soon get fed up with a chattering relay, though :).
 

crutschow

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Most Helpful Member
Thanks crutschow and alec_t, but any relay can do this (close when there has pulse, open when there has no pulse)? the pulse is about 47V, 3 pulses per revolution (Isink max = 10 mA), thanks!
If you think you already know the solution then why are you asking us? :confused:
 

MikeMl

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The TS should post a circuit of how to do this with a relay. Inquiring minds want to know.
 

AnalogKid

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Thanks crutschow and alec_t, but any relay can do this (close when there has pulse, open when there has no pulse)?
If you mean 'can any relay do this?', then no. There are hundreds of pulses per second, and you don't want something that responds to each pulse, but to the string of pulses.

Almost all fan monitors are based on the same circuit, similar to the one Wally posted. If you don't want to build one, you can buy one:

http://controlresources.com/fan-alarm-fan-failure-alarm-monitoring/

ak
 

Nigel Goodwin

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While the OP doesn't specify his location, it seems pretty obvious that English isn't his first language - and he's actually ASKING if it can be done with a relay, rather than stating that it can be.
 

MikeMl

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A EC Fan output a signal 3 pulses per revolution (Isink max = 10 mA), please advise a device to change this signal to on/off signal so that output ON when the Fan is running and OFF when the Fan is not running.
Let me know a specific model would be greatly appreciated because I am green for electronic, thanks!
What is the system Voltage? 12Vdc?
As the fan RPM slows down, at what RPM do you want the output signal to change from ON to OFF?
Is there a requirement to actually use a relay?
What load is the speed detector driving?

We need to know the answer to these questions regardless if you make or buy.
 
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crutschow

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While the OP doesn't specify his location, it seems pretty obvious that English isn't his first language - and he's actually ASKING if it can be done with a relay, rather than stating that it can be.
Since it's the policy of this site to make it easy for posters to not give their location, then I'll leave it to you to interpret such things. :rolleyes:
 

h_h

New Member
If you mean 'can any relay do this?', then no. There are hundreds of pulses per second, and you don't want something that responds to each pulse, but to the string of pulses.

Almost all fan monitors are based on the same circuit, similar to the one Wally posted. If you don't want to build one, you can buy one:

http://controlresources.com/fan-alarm-fan-failure-alarm-monitoring/

ak

Thanks AnalogKid, appreciate you give me example (fan monitors), because I have no idea what device can to do this and not much knowledge about this.
 

h_h

New Member
What is the system Voltage? 12Vdc?
As the fan RPM slows down, at what RPM do you want the output signal to change from ON to OFF?
Is there a requirement to actually use a relay?
What load is the speed detector driving?

We need to know the answer to these questions regardless if you make or buy.
Thanks MikeMl, zero RPM change to OFF, greater than zero RPM change to ON, power supply for the Fan is 48Vdc, so, I will use a transformer to supply 48Vdc.
According to the spec. of the Fan, it seems output the pulses with 47V.
 

h_h

New Member
While the OP doesn't specify his location, it seems pretty obvious that English isn't his first language - and he's actually ASKING if it can be done with a relay, rather than stating that it can be.
Yes, my English is not well. At the beginning, I was wonder the relay can do this.
 

AnalogKid

Well-Known Member
Most Helpful Member
What are the manufacturer and the part number for the fan?

Usually a 48V fan has a tach output limited to 12 V or 24 V peak, or an open collector output so you can set your own peak voltage. The tach signal comes from a Hall Effect magnetic field sensor near the motor's rotating magnets, and is good for only around 10 mA. If the tach pulses really are 48 V peak, that is not a problem, just something to address in the circuit. Also, there usually are an even number of pulses per revolution. Are you sure about three?

What kind of "on/off" signal do you need? Does it have to be isolated from the fan power, or have to deliver very much current, or light an LED, or what?

This can monitor one to three fans:
http://controlresources.com/tachscan-3/

This monitors one fan per board. You can snap off as many as you need:
http://controlresources.com/tachstrip/

Note that both of those boards are limited to a maximum of 24 V power and 24 V input pulses.

Please ignore Colin's "advice". Simply attaching a relay coil to a power supply will do nothing to monitor the frequency of a low-energy pulsing signal.

ak
 
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Colin

Active Member
What are you saying AnalogKid ????
Please ignore Colin's "advice". Simply attaching a relay coil to a power supply will do nothing to monitor the frequency of a low-energy pulsing signal.

His requirement is:

an output ON when the Fan is running and OFF when the Fan is not running.
 

alec_t

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His requirement is:
an output ON when the Fan is running and OFF when the Fan is not running.
But 'Fan is running' is not the same as 'Power to the fan is switched ON'. Presumably he wants to check for fan failure.
 

AnalogKid

Well-Known Member
Most Helpful Member
What are you saying AnalogKid ????
Please ignore Colin's "advice". Simply attaching a relay coil to a power supply will do nothing to monitor the frequency of a low-energy pulsing signal.

His requirement is:

an output ON when the Fan is running and OFF when the Fan is not running.
His requirement is in post #4 and post #14, both of which preceded your response.

ak
 
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