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A latching relay question

G

garyr

Jan 1, 1970
0
I'm using a latching relay to switch between two gain-setting resistors for
an instrumentation amplifier (INA128). There are two such amplifiers on my
board, hence two relays. I would like to connect the set and reset coils
of both relays in parallel and switch both at the same time. Latching
relay guidelines I found on the Panasonic site states that if the coils in
two latching relays are connected in parallel, there should be a diode in
series with each. It doesn't say why this is necessary and the diagram that
illustrates this doesn't show any snubbers in parallel with the coils. Would
the series diodes be necessary if snubber diodes were connected in parallel
with each coil?
 
M

Mark

Jan 1, 1970
0
I'm using a latching relay to switch between two gain-setting resistors for
an instrumentation amplifier (INA128). There are two such amplifiers on my
board, hence two relays. I would like to connect the set and reset coils
of both relays in parallel and switch both at the same time. Latching
relay guidelines I found on the Panasonic site states that if the coils in
two latching relays are connected in parallel, there should be a diode in
series with each. It doesn't say why this is necessary and the diagram that
illustrates this doesn't show any snubbers in parallel with the coils. Would
the series diodes be necessary if snubber diodes were connected in parallel
with each coil?

maybe there can be unwanted coupling between the set and reset coils
such that when you pulse say the set coil of RL1 it may feed some
energy though the interconnected reset coils and create an unwanted
reset to RL2. In your specific case since BOTH set and reset are
connected in parallel, it probably won't be a problem. In other cases
where they are only partially interconnected, there might be unwanted
state changes.

From the construction of the relay, does it look like there could be
significant coupling between the set and reset coils?

Mark
 
O

OldeGuye

Jan 1, 1970
0
After serious thinking garyr wrote :
I'm using a latching relay to switch between two gain-setting resistors for
an instrumentation amplifier (INA128). There are two such amplifiers on my
board, hence two relays. I would like to connect the set and reset coils
of both relays in parallel and switch both at the same time. Latching
relay guidelines I found on the Panasonic site states that if the coils in
two latching relays are connected in parallel, there should be a diode in
series with each. It doesn't say why this is necessary and the diagram that
illustrates this doesn't show any snubbers in parallel with the coils. Would
the series diodes be necessary if snubber diodes were connected in parallel
with each coil?

Don't the diodes act a balancing ballasts too?
 
S

Syd Rumpo

Jan 1, 1970
0
I'm using a latching relay to switch between two gain-setting resistors for
an instrumentation amplifier (INA128). There are two such amplifiers on my
board, hence two relays. I would like to connect the set and reset coils
of both relays in parallel and switch both at the same time. Latching
relay guidelines I found on the Panasonic site states that if the coils in
two latching relays are connected in parallel, there should be a diode in
series with each. It doesn't say why this is necessary and the diagram that
illustrates this doesn't show any snubbers in parallel with the coils. Would
the series diodes be necessary if snubber diodes were connected in parallel
with each coil?

Just in case you didn't know, latching relays (at least the ones I've
used) have a minimum physical separation - if they're too close, the
magnetics can interfere.

Cheers
 
G

garyr

Jan 1, 1970
0
John Larkin said:
Can't see why you can't just parallel them. The extra diodes make no
sense.

We use this to drive small latching relays:

https://dl.dropboxusercontent.com/u/53724080/Circuits/V490_Relay_Driver.jpg



--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

I like your scheme; much simpler that what I had in mind.

What is the purpose of Q1 and Q2 in your schematic?

Many thanks.
 
G

garyr

Jan 1, 1970
0
I'm using a latching relay to switch between two gain-setting resistors
for
an instrumentation amplifier (INA128). There are two such amplifiers on my
board, hence two relays. I would like to connect the set and reset coils
of both relays in parallel and switch both at the same time. Latching
relay guidelines I found on the Panasonic site states that if the coils in
two latching relays are connected in parallel, there should be a diode in
series with each. It doesn't say why this is necessary and the diagram
that
illustrates this doesn't show any snubbers in parallel with the coils.
Would
the series diodes be necessary if snubber diodes were connected in
parallel
with each coil?

maybe there can be unwanted coupling between the set and reset coils
such that when you pulse say the set coil of RL1 it may feed some
energy though the interconnected reset coils and create an unwanted
reset to RL2. In your specific case since BOTH set and reset are
connected in parallel, it probably won't be a problem. In other cases
where they are only partially interconnected, there might be unwanted
state changes.

From the construction of the relay, does it look like there could be
significant coupling between the set and reset coils?

Mark

The relays are sealed so there no way to determine how they are constructed.
 
G

garyr

Jan 1, 1970
0
Syd Rumpo said:
Just in case you didn't know, latching relays (at least the ones I've
used) have a minimum physical separation - if they're too close, the
magnetics can interfere.

Cheers

In my case they will be about one inch apart. Is that enough?
 
J

Jasen Betts

Jan 1, 1970
0
Don't the diodes act a balancing ballasts too?

no. the relays resistance and inductance do a better job of that.
 
S

Syd Rumpo

Jan 1, 1970
0
In my case they will be about one inch apart. Is that enough?

Well, it'll be in the data sheet, but yes, one inch will be plenty.

Cheers
 
G

garyr

Jan 1, 1970
0
I started changing my schematic to control the relays using your method and
realized that I could do the same thing with two inverter gates. I must be
missing something; what is the reason for using two 2-input nor gates?
 
On Sunday, April 21, 2013 4:31:51 PM UTC-4, garyr wrote:

Diodes in series with each coil will prevent a sneak circuit from the COM though the coil of the first relay then back into the coil of the second relay through it to its COM ( if that is the configuration you're dealing with). I can see where there could possibly be this interaction via magnetic coupling within the relay so that the relays end up interfering with each other if the turn-off dynamics are not exactly identical. So, it is not a bad idea, diodes are cheap, use them.
 
types. Otherwise, I can't imagine what the series diodes accomplish.

The diodes block current in the mesh of the two coils in series through the relay coil COM node. Obviously Panasonic ran into the problem before. If he doesn't have the headroom for diodes then he has two go with four separate drivers.
 
G

garyr

Jan 1, 1970
0
John Larkin said:
On Tue, 23 Apr 2013 13:07:43 -0700 (PDT),


I guess so. The circuit is easily fudged for the 2-coil case. This
gate thing is for addressing a large matrix of 1-coil latching relays.
You could do an X-Y drive matrix, with series diodes, to mux 2-coil
types. Otherwise, I can't imagine what the series diodes accomplish.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

I switched to a one-coil relay.

Thanks again to all who replied to my query.
 
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