Latching relays

[pozz]

I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

 

[Michael Terrell]

On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:

.

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?

 

[pozz]

Il 24/09/2019 13:03, Michael Terrell ha scritto:

On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:
I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?

Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

 

[Michael Terrell]

On Tuesday, September 24, 2019 at 9:00:06 AM UTC-4, pcdh...@gmail.com wrote:

   I am currently designing a replacement 'A23' Attenuator board for
the HP3325A/B function generators. The original relays are long obsolete
so rather than making adapter boards, I am designing a smaller board that
uses modern relays.

If you're getting a bunch made, I'd chip in for three of them. That's the only thing that seems to go bad on those things. So far Deoxit has always fixed it, but I expect it's just a matter of time.

Cheers

Phil Hobbs

I need at least three for myself. I was looking at making ten boards, with a choice of Phono or SMA connectors. If you have a failed board you can reuse the resistors, but I am planning to use SMD for complete boards. I may also make a replacement for the HV output board, and the 10 MHz OCXO as well. I have a pile of them that are missing one or more of those three boards.

 

   I am currently designing a replacement 'A23' Attenuator board for
the HP3325A/B function generators. The original relays are long obsolete
so rather than making adapter boards, I am designing a smaller board that
uses modern relays.

If you're getting a bunch made, I'd chip in for three of them. That's the only thing that seems to go bad on those things. So far Deoxit has always fixed it, but I expect it's just a matter of time.

Cheers

Phil Hobbs

 

[Michael Terrell]

On Tuesday, September 24, 2019 at 8:06:18 AM UTC-4, pozz wrote:

Il 24/09/2019 13:03, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:
I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?


Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

My point was, there is no reason to continue to power a latching relay. Look at the current draw, vs a non latching version. It takes more power to set or reset a mechanical latch, It doesn't matter if the relay is single or double coil. Why waste power and heat up the relay? That will shorten its useful life.

I am currently designing a replacement 'A23' Attenuator board for the HP3325A/B function generators. The original relays are long obsolete so rather than making adapter boards, I am designing a smaller board that uses modern relays. It will also allow you to select the supply voltage for the relays, to allow the use of more common voltages.

 

[pozz]

Il 24/09/2019 14:51, Michael Terrell ha scritto:

On Tuesday, September 24, 2019 at 8:06:18 AM UTC-4, pozz wrote:
Il 24/09/2019 13:03, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:
I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?


Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

My point was, there is no reason to continue to power a latching relay.

I have two reasons.

The first is the software that must be more complex to generate an
impulse instead of setting/resetting an output pin level forever.

I know, it's simple to create a pulse too with a blocking delay:

activate_coil1();
delay_ms(10);
deactivate_coil1();

however in my software, that is cooperative multitasking, I can't block
for more than 100usec. I need to implement a small state-machine to
generate a pulse.

The other reason is: how long should be the impulse? Datasheet says
maximum 3ms, just to be sure I would generate a 10ms pulse. Could I be
sure the relay has switching after my pulse? I don't have any feedback
from relay.

In my application it's much more important to be sure that the relay has
switched instead of saving some power.


> Look at the current draw, vs a non latching version. It takes more power to set or reset a mechanical latch, It doesn't matter if the relay is single or double coil.

8.3mA vs 12.5mA

> Why waste power and heat > up the relay? That will shorten its useful life.

It's a pity the datasheet says nothing about expected life vs coil
activation time.

I am currently designing a replacement 'A23' Attenuator board for the HP3325A/B function generators. The original relays are long obsolete so rather than making adapter boards, I am designing a smaller board that uses modern relays. It will also allow you to select the supply voltage for the relays, to allow the use of more common voltages.

 

On Tue, 24 Sep 2019 09:04:17 +0200, pozz <pozzugno@gmail.com> wrote:

.

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Looks OK to me. The coil power is not excessive and the data sheet
doesn't restrict on time.

We like to blip latching relays to reduce thermoelectric offsets.

 

[Michael Terrell]

On Tuesday, September 24, 2019 at 9:40:30 AM UTC-4, pozz wrote:

Il 24/09/2019 14:51, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 8:06:18 AM UTC-4, pozz wrote:
Il 24/09/2019 13:03, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:
I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?


Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

My point was, there is no reason to continue to power a latching relay.

I have two reasons.

The first is the software that must be more complex to generate an
impulse instead of setting/resetting an output pin level forever.

I know, it's simple to create a pulse too with a blocking delay:

activate_coil1();
delay_ms(10);
deactivate_coil1();

however in my software, that is cooperative multitasking, I can't block
for more than 100usec. I need to implement a small state-machine to
generate a pulse.

Look at 'Pulse stretcher' circuits.

The other reason is: how long should be the impulse? Datasheet says
maximum 3ms, just to be sure I would generate a 10ms pulse. Could I be
sure the relay has switching after my pulse? I don't have any feedback
from relay.

Either you trust the relay, or you find another way to design the item. If the datasheet says the maximum is 3ms, you don't need 10ms.

In my application it's much more important to be sure that the relay has
switched instead of saving some power.


Look at the current draw, vs a non latching version. It takes more power to set or reset a mechanical latch, It doesn't matter if the relay is single or double coil.

8.3mA vs 12.5mA

Why waste power and heat > up the relay? That will shorten its useful life.

Implement the timing in the driver circuit. How cay you trigger the second coil. if you are still powering the first coil?

It's a pity the datasheet says nothing about expected life vs coil
activation time.

 

[Gerhard Hoffmann]

I don't think that keeping one side powered forever will work.

Cut and paste from the Teledyne RS-170 bistable relay data sheet:

%< ----- %< ----- %< ----- %< ----- %< ----- %< ----- %< -----
Since operation depends upon cancella-
tion of a magnetic field, it is necessary
to apply the correct polarity to the relay coils as indicated on the
relay schematic.
When latching relays are installed in equipment, the latch and reset
coils should not be
pulsed simultaneously. Coils should not be pulsed with less than the
nominal coil volt-
age and the pulse width should be a minimum of three times the specified
operate time
of the relay. If these conditions are not followed, it is possible for
the relay to be in the
magnetic neutral position.
%< ----- %< ----- %< ----- %< ----- %< ----- %< ----- %< -----

.... etc. I can't paste the graphics on usenet.

regards, Gerhard

 

[Gerhard Hoffmann]

Am 24.09.19 um 18:47 schrieb Gerhard Hoffmann:

Am 24.09.19 um 18:41 schrieb Gerhard Hoffmann:

RF-170, not RS-170


https://www.mouser.de/ProductDetail/Teledyne-Relays/RF170?qs=6qHLyUDW%2FdUtYJXDGa1I5Q==
  

Ingrid says:

The Mouser web site points into nirvana.

<
https://4donline.ihs.com/images/VipMasterIC/IC/TELD/TELDS00246/TELDS00246-1.pdf?hkey=52A5661711E402568146F3353EA87419

(Ingrid was someone in the German sub-internet. You could see
her thinking in endless series of posts.)

 

[amdx]

On 9/24/2019 11:29 AM, jlarkin@highlandsniptechnology.com wrote:

On Tue, 24 Sep 2019 09:04:17 +0200, pozz <pozzugno@gmail.com> wrote:

I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Looks OK to me. The coil power is not excessive and the data sheet
doesn't restrict on time.

We like to blip latching relays to reduce thermoelectric offsets.

Oh good, you brought it up!
I read this on the data sheet, "Low thermal electromotive force(approx.
5 ÎźV)"
Where is this developed? is it between the contacts?
Is it heat from the coil getting to the contact arms?

Mikek

 

[Gerhard Hoffmann]

Am 24.09.19 um 18:41 schrieb Gerhard Hoffmann:

RF-170, not RS-170

<
https://www.mouser.de/ProductDetail/Teledyne-Relays/RF170?qs=6qHLyUDW%2FdUtYJXDGa1I5Q==
>

 

[Dimitrij Klingbeil]

On 2019-09-24 19:21, amdx wrote:

On 9/24/2019 11:29 AM, jlarkin@highlandsniptechnology.com wrote:

We like to blip latching relays to reduce thermoelectric offsets.


Oh good, you brought it up!
I read this on the data sheet, "Low thermal electromotive force(approx.
5 ÎźV)"
Where is this developed? is it between the contacts?
Is it heat from the coil getting to the contact arms?

From the application point of view, it looks like between the contacts.

In reality, there are thermal gradients and dissimilar metal junctions
in multiple places and the value indicated in the data sheet should be a
sum total for the relay as a whole.

There is likely a bimetal junction at each contact: the arms are made
from a flexible material and the contact points are made from another,
typically softer non-oxidizing material (and sometimes plated too).

Since the arms tend to be at unequal temperatures (one arm is nearer to
the coil and the thermal interface between arms is poor because they can
only touch at a tiny spot), each touching contact pair ends up being a
reverse-series of 2 thermocouples at different temperatures.

There are also other pairs of bimetal interfaces at the solder joints
between the relay and the circuit board. The relay partially heatsinks
itself through its pins, and since the pins have unequal values of
thermal conductivity from the heat source, they end up at different
temperatures at the solder joints too.

Also, the arms might not be made from one piece of metal internally.

The method of mounting can also make a difference, such as soldering one
pin into a large plane area and another to a tiny trace. This will
heatsink the pins at different thermal conductivities to the ambient,
and the result can drive a temperature difference between the joints.

Regards, Dimitrij

 

[John Larkin]

On Tue, 24 Sep 2019 12:21:44 -0500, amdx <nojunk@knology.net> wrote:

On 9/24/2019 11:29 AM, jlarkin@highlandsniptechnology.com wrote:
On Tue, 24 Sep 2019 09:04:17 +0200, pozz <pozzugno@gmail.com> wrote:

I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Looks OK to me. The coil power is not excessive and the data sheet
doesn't restrict on time.

We like to blip latching relays to reduce thermoelectric offsets.


Oh good, you brought it up!
I read this on the data sheet, "Low thermal electromotive force(approx.
5 ?V)"
Where is this developed? is it between the contacts?
Is it heat from the coil getting to the contact arms?

Mikek

An energized coil gets hot and makes thermal gradients everywhere.
Thermoelectrics can happen at the contacts, all the internal
conductors and hinges and stuff, leads, and solder joints to the PC
board. Small telecom type relays can make 10s of microvolts of offset.

This board uses one dual NOR gate per relay. There are lots of
relays+nor gates arranged in a matrix. We set or clear 8 at a time.

https://www.dropbox.com/s/s6suef3n2ml7b2e/V490_Relay_Driver.jpg?raw=1

 

On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:

.

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

HP wants the RF relay to be electromagnetically dead when it passes signals to avoid low level nonlinear distortion that may result. But that will be the least of your challenges in a fitting a new board, depending on how much of an instrument you want.

 

[Clifford Heath]

On 24/9/19 10:51 pm, Michael Terrell wrote:

I am currently designing a replacement 'A23' Attenuator board for the HP3325A/B function generators. The original relays are long obsolete so rather than making adapter boards, I am designing a smaller board that uses modern relays. It will also allow you to select the supply voltage for the relays, to allow the use of more common voltages.

Bit bloody easier to use a modern approach, like
https://octopart.com/search?q=PE43712

Clifford Heath.

 

On Tuesday, September 24, 2019 at 9:40:30 AM UTC-4, pozz wrote:

Il 24/09/2019 14:51, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 8:06:18 AM UTC-4, pozz wrote:
Il 24/09/2019 13:03, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:
I have to use a latching relay with two coils, exactly TQ2-L2-24V[1]..

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?


Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

My point was, there is no reason to continue to power a latching relay.

I have two reasons.

The first is the software that must be more complex to generate an
impulse instead of setting/resetting an output pin level forever.

I know, it's simple to create a pulse too with a blocking delay:

activate_coil1();
delay_ms(10);
deactivate_coil1();

however in my software, that is cooperative multitasking, I can't block
for more than 100usec. I need to implement a small state-machine to
generate a pulse.

The other reason is: how long should be the impulse? Datasheet says
maximum 3ms, just to be sure I would generate a 10ms pulse. Could I be
sure the relay has switching after my pulse? I don't have any feedback
from relay.

In my application it's much more important to be sure that the relay has
switched instead of saving some power.


Look at the current draw, vs a non latching version. It takes more power to set or reset a mechanical latch, It doesn't matter if the relay is single or double coil.

8.3mA vs 12.5mA

Why waste power and heat > up the relay? That will shorten its useful life.

It's a pity the datasheet says nothing about expected life vs coil
activation time.


I am currently designing a replacement 'A23' Attenuator board for the HP3325A/B function generators. The original relays are long obsolete so rather than making adapter boards, I am designing a smaller board that uses modern relays. It will also allow you to select the supply voltage for the relays, to allow the use of more common voltages.

Ummmm, this operation is very strange. What CPU are you using? Almost all of them have a timer capability. Write a '1' to the DO port associated with the relay and at the same time, set time to count down x ms. The ISR associated with the timer can write a '0' to the DO port. Doesn't matter if you have an RTOS, a roll your own task scheduler, or a cyclic exec or a big loop. or, make the entire system event driven. No hw timer on the cpu? use the timer or RTC function associated with the RTOS. Busy-waits are inefficient - there is almost no reason to use them. Also, a loop with a gazillion no-ops to implement time related events makes for non-portable code.
Sorry, but your reasons are invalid.

No feedback from the relay? So this is a fundamental design issue. If it is imperative that you know the state of the relay, then feedback should have been incorporated into the design. The relay state could be run into a bit on the interrupt register.
Can the state be inferred from some other state variable?
Connect a 555 as a monstable one shot to do the pulse function.
Don't *have* to know the relay state, then energize for 2x what ever the data sheet says, 'just to be sure.'

Since you have a multi tasking OS, run a thread to turn the relay on when necessary. Make the worst case execution time = period = 2x the data sheet pulse width. Create a on/off state machine in the thread that services the relay. Make the thread dispatch based on a relay_on event. Do schedualability analysis to make sure all the threads are scheduable with the inclusion of a sporadic event thread. Check to make sure priority inversion can't happen.
Any embedded micro designed in the last 30 years most always has a hw timer..
Good luck
J

 

[pozz]

Il 25/09/2019 05:20, jjhudak4@gmail.com ha scritto:

On Tuesday, September 24, 2019 at 9:40:30 AM UTC-4, pozz wrote:
Il 24/09/2019 14:51, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 8:06:18 AM UTC-4, pozz wrote:
Il 24/09/2019 13:03, Michael Terrell ha scritto:
On Tuesday, September 24, 2019 at 3:04:22 AM UTC-4, pozz wrote:
I have to use a latching relay with two coils, exactly TQ2-L2-24V[1].

Is it possible to give power to only one coil forever, as in a "normal"
relay, or is it better to remove power from coils after a short time?

I don't have critical restrictions on power consumption, so I'm going to
maintain one coil active forever (until power is cut off).
Are there any drawback on this approach?


[1] https://www.mouser.it/datasheet/2/315/mech_eng_tq-1299280.pdf

Why use a latching relay, if you plan on keeping it energized?


Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

My point was, there is no reason to continue to power a latching relay.

I have two reasons.

The first is the software that must be more complex to generate an
impulse instead of setting/resetting an output pin level forever.

I know, it's simple to create a pulse too with a blocking delay:

activate_coil1();
delay_ms(10);
deactivate_coil1();

however in my software, that is cooperative multitasking, I can't block
for more than 100usec. I need to implement a small state-machine to
generate a pulse.

The other reason is: how long should be the impulse? Datasheet says
maximum 3ms, just to be sure I would generate a 10ms pulse. Could I be
sure the relay has switching after my pulse? I don't have any feedback
from relay.

In my application it's much more important to be sure that the relay has
switched instead of saving some power.


Look at the current draw, vs a non latching version. It takes more power to set or reset a mechanical latch, It doesn't matter if the relay is single or double coil.

8.3mA vs 12.5mA

Why waste power and heat > up the relay? That will shorten its useful life.

It's a pity the datasheet says nothing about expected life vs coil
activation time.


I am currently designing a replacement 'A23' Attenuator board for the HP3325A/B function generators. The original relays are long obsolete so rather than making adapter boards, I am designing a smaller board that uses modern relays. It will also allow you to select the supply voltage for the relays, to allow the use of more common voltages.


Ummmm, this operation is very strange. What CPU are you using? Almost all of them have a timer capability. Write a '1' to the DO port associated with the relay and at the same time, set time to count down x ms. The ISR associated with the timer can write a '0' to the DO port. Doesn't matter if you have an RTOS, a roll your own task scheduler, or a cyclic exec or a big loop. or, make the entire system event driven. No hw timer on the cpu? use the timer or RTC function associated with the RTOS. Busy-waits are inefficient - there is almost no reason to use them. Also, a loop with a gazillion no-ops to implement time related events makes for non-portable code.
Sorry, but your reasons are invalid.

I didn't say I can't implement a software that generates a pulse, I said
that this implementation is more complex compared to set/reset a pin.
I know how to code a software that generates a pulse, however I like to
keep the code simple if possible (bugs are everywhere).

No feedback from the relay? So this is a fundamental design issue. If it is imperative that you know the state of the relay, then feedback should have been incorporated into the design. The relay state could be run into a bit on the interrupt register.
Can the state be inferred from some other state variable?
Connect a 555 as a monstable one shot to do the pulse function.
Don't *have* to know the relay state, then energize for 2x what ever the data sheet says, 'just to be sure.'

Since you have a multi tasking OS, run a thread to turn the relay on when necessary. Make the worst case execution time = period = 2x the data sheet pulse width. Create a on/off state machine in the thread that services the relay. Make the thread dispatch based on a relay_on event. Do schedualability analysis to make sure all the threads are scheduable with the inclusion of a sporadic event thread. Check to make sure priority inversion can't happen.
Any embedded micro designed in the last 30 years most always has a hw timer.
Good luck
J

 

[legg]

On Tue, 24 Sep 2019 14:06:14 +0200, pozz <pozzugno@gmail.com> wrote:

<snip>

Why use a latching relay, if you plan on keeping it energized?


Thanks for the answer, even if it doesn't answer my question.

It's very simple, because I want a stable condition when the power is
cut off. Latching relays guarantees that the contacts don't change their
position when the mains power goes down.

This is a 'Who's on first. joke, in reverse.

You can only guarantee a powerless logic state in hardware by starting
your design with that physical state. Even then, you can't count on
such a configuration to provide user safety under single fault
conditions.

If you want to 'control' with no power, you need a second power
source, even if it's only an unlatched spring.

Latching relays sole function is as memory of their last controlled
power state, so you can't use them for a fail-safe.

If you want a safe power-off, you need physical guards and a dedicated
kill switch that provides that feature.

RL