Author Topic: DMM controls  (Read 1762 times)

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Offline Fungus

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Re: DMM controls
« Reply #25 on: April 28, 2021, 06:31:27 am »
Many handheld DMMs use relays. For example, the Keysight U1252B.

Yep. There's even some cheapo Anengs with relays inside them.
 

Offline HKJ

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Re: DMM controls
« Reply #26 on: April 28, 2021, 07:08:39 am »
Many handheld DMMs use relays. For example, the Keysight U1252B.

Yep. There's even some cheapo Anengs with relays inside them.

The cheap DMM's uses a single power hungry relay, the DMM's I posted before uses a few pulse controlled relays, that is a bit more tricky to control, but do not use any power in either position. Bench meters usually have more relays and will often use the power hungry version (344xxA series use 3 pulse controlled relays, DMM6500 uses 6, probably the power hungry type, same with East Tester ET3240, Siglent SDM3045X uses 5).

It is possible to make handheld DMM's with buttons as can be seen on my photo above, but it is not the same as bench meters, they are designed differently. Using relays will usually increase power consumption and that is not something that is wanted in a good handheld DMM (But the cheap Chinese do not care). Gossen have succeeded in keeping the power consumption low, even with relays, but not everybody like their solution (See what Joe says about a Gossen meter).
 

Offline shakalnokturn

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Re: DMM controls
« Reply #27 on: April 28, 2021, 07:22:29 am »
Other than added complexity would there be a good reason not to use static relays?
 

Offline HKJ

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Re: DMM controls
« Reply #28 on: April 28, 2021, 07:32:45 am »
Other than added complexity would there be a good reason not to use static relays?

They are sensitive to high magnetic field, i.e. a hanger for a DMM may change the relay making the DMM show a wrong value.
 

Offline 2N3055

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Re: DMM controls
« Reply #29 on: April 28, 2021, 07:33:20 am »
Other than added complexity would there be a good reason not to use static relays?

They do. Metrix does, Gossen does.. That is why JoeQ could confuse them with permanent magnets...
 

Offline HKJ

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Re: DMM controls
« Reply #30 on: April 28, 2021, 08:03:33 am »
Other than added complexity would there be a good reason not to use static relays?

They do. Metrix does, Gossen does.. That is why JoeQ could confuse them with permanent magnets...

I have not seen Joe confuse a Chauvin Arnoux meter, they may be susceptible for magnetic interference or they may have added protection against it. There are two way to protect: Magnetic shielding or a position sense connection from the relay to the processor.
The only guy I have ever heard about having problems with the relays is Joe, maybe because these meters are seldom used on a hanger.

Note: Chauvin Arnoux is the brand behind Metrix and manufactures the meters.
 

Offline spanakop

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Re: DMM controls
« Reply #31 on: April 28, 2021, 08:08:31 am »
I Cymaphore has a good point here.
... accidentially pressing one of those many buttons or pressing the wrong one can be a real showstopper.

Rotary switches that can be single hand operated and that tell you about the selected range in a haptic way are superior in such an environment.

However, there are already protection mechanisms in place for accidentally activating or leaving a current measurement when you really want voltage for example (I have done this long a go, I wasn't paying attention, wasn't a pretty sight, lesson learn't there :palm:).

There are many electronic devices that have moved away from mechanical designs or have been replaced by better designs altogether; cassettes, video players, spinny hardrives, radios etc off the top of my head. Even oscilloscopes. Gone is the CRT potentiometers, lever switches, now you have digital displays and rotary encoders. How many devices have a mechanical switch for powering on, a lot are simple push buttons now. I'm sure there are other examples.

By removing the dial, you can also make it a little more compact, that dial and the supporting PCB tracks, take up a lot of room. That space could be taken up by a bigger display perhaps, more functions.

I haven't got any objection to rotary dials, I do like the Brymen DMM's, I just think in this day and age they are not really needed anymore. It has been done already for some meters, I think they need to move forward and innovate a little more.
 

Offline HKJ

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Re: DMM controls
« Reply #32 on: April 28, 2021, 08:37:22 am »
There are many electronic devices that have moved away from mechanical designs or have been replaced by better designs altogether; cassettes, video players, spinny hardrives, radios etc off the top of my head. Even oscilloscopes. Gone is the CRT potentiometers, lever switches, now you have digital displays and rotary encoders. How many devices have a mechanical switch for powering on, a lot are simple push buttons now. I'm sure there are other examples.

It is not always these changes are a advantage, like the soft power button that means the device uses power all the time, or a pushbutton that requires a lot of presses to select a value, instead of a rotary switch that can be directly turned to the desired position.


By removing the dial, you can also make it a little more compact, that dial and the supporting PCB tracks, take up a lot of room. That space could be taken up by a bigger display perhaps, more functions.

Look at the photos I posted: The CA has space enough for a rotary dial and it has a very large display. The Gossen with a rotary dial is the most advanced meter of the four by a good margin.
My guess on why CA uses buttons is because it can be fully computer controlled and then the switch would not match the actual function (Gossen have that issue).

I haven't got any objection to rotary dials, I do like the Brymen DMM's, I just think in this day and age they are not really needed anymore. It has been done already for some meters, I think they need to move forward and innovate a little more.

Dials are a very effective way to select and adjust settings, often way superior to switches, using buttons may make a meter harder to use. I am using the CA as my main meter at the current time and I do not see the buttons as any advantage.
 

Offline shakalnokturn

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Re: DMM controls
« Reply #33 on: April 28, 2021, 08:49:32 am »
Other than added complexity would there be a good reason not to use static relays?

They do. Metrix does, Gossen does.. That is why JoeQ could confuse them with permanent magnets...

A bistable (mechanical) relay and static (semiconductor) relay are different devices.
AFAIK bistable relays are used in some handheld DMM's.
It will take a hell of a permanent magnet to confuse a static relay though...
 

Offline HKJ

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Re: DMM controls
« Reply #34 on: April 28, 2021, 09:48:34 am »
A bistable (mechanical) relay and static (semiconductor) relay are different devices.

I have never hard solid state relays called static before and they are not very static, they require a few mA to turn on and stay turned on, this will often double the power consumption on a DMM.
The mosfets used to handle current shunts are not relays, they are not isolated and do not need any power to stay on.
 

Offline 2N3055

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Re: DMM controls
« Reply #35 on: April 28, 2021, 10:06:36 am »

It will take a hell of a permanent magnet to confuse a static relay though...

Hehehe that is true..

Sorry, I didn't understand you meant SSD by static relay..
True, SSD is less power than bistable magnetic, but still some consumption..
For slow changes, bistable magnetic average consumption converges to 0....
 

Offline Cymaphore

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Re: DMM controls
« Reply #36 on: April 28, 2021, 12:52:35 pm »
If one works with electronics in a lab environment, magnetic interference, HRC-fuses and even shielding is in many cases not even a thing. Nice to have, but no problem. You probably care more about high resolution, precision and such things.

If one works with synchronous motors and traction inverters, you usually prefer shielding and fuses over digit-count.

It's all about the intended use case.

That's why so many people out there are frequently complaining about HVAC and electrician meters (too few counts, AC comes first, missing duty cycle, etc., etc.). These are usually not "general purpose" meters, but rather focus on very specific use cases and take care of specific needs.

Same with buttons vs. rotary switches. I don't think one of those solutions is generally better than the other. It depends on what it's used for and how it needs to be operated.
 
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Offline BeBuLamar

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Re: DMM controls
« Reply #37 on: April 28, 2021, 01:29:12 pm »
Whenever I used the Fluke 287 or 289 I always turn it off when trying to turn on the back light. They put the power on/off button right where the backlight button is on the 87V. Also it takes me a second to realize that I have to turn it on with the button and not the dial.
 

Offline David Hess

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Re: DMM controls
« Reply #38 on: April 29, 2021, 09:46:58 pm »
A mechanical switching has advantages over electronic switching unless relays are used, and relays are expensive.
 


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