The component SCA 550, would you confirm this is a varistor? I cannot find any datasheet on this particular model/component n umber..?

Thanks in advance !

 

Looks like a capacitor to me. Why do you think it is a varistor?

 

Looks like a capacitor to me. Why do you think it is a varistor?

On the pcb it has an R designation,..its part of the current input protection on this dmm circuit, since a varistor is a voltage dependent resistor (VDR) that's my guess...??

Looks like a capacitor to me. Why do you think it is a varistor?

Looks like a capacitor to me. Why do you think it is a varistor?

 

How is it connected? From the photograph it seems connected to one leg of the thermistor on the right, but I can't tell for sure.
It certainly has the shape of either a MOV or a capacitor. Capacitors are usually not placed close to the input terminals of a DMM.

 

Exactly, that's why I do not believe it's a cap. It's located on the current input protection side of the multimeter.

 

Might be a self resettable fuse since you say it's located on the current input.
SG

 

Looks like an MOV. Can you measure it at all? Does it change when you heat it up, cool it down??

 

How is it connected? From the photograph it seems connected to one leg of the thermistor on the right, but I can't tell for sure.
It certainly has the shape of either a MOV or a capacitor. Capacitors are usually not placed close to the input terminals of a DMM.

 

Might be a self resettable fuse since you say it's located on the current input.
SG

Nope, it already has 2 ceramic fuses, 1 mA and 1A would make no sense to add a resettable fuse to the mix..

 

High temperature, military grade capacitor, page 3.


EDIT:
Definitely SCA-550 is THERMISTOR:
http://dvtecnologia.com.br/imagens/SCA.pdf

 

High temperature, military grade capacitor, page 3.

View attachment 169005

Hmmm, why use a military grade cap on an 8$ multimeter?

 

EDIT:
Definitely SCA-550 is THERMISTOR:
http://dvtecnologia.com.br/imagens/SCA.pdf

That is definitely much more consistent with the application. Thanks for sharing.

 

So all things considered this cheap dmm had some decent input protection..thanks for everyones input!

 

Just be mindful of the following: there is a lot more to a DMM's input protection than the parts themselves. Not only the routing matters (I have seen fuses in series with the voltage jack, for example) but, depending on the nature of the event, a transient may go right through protection devices such as MOVs and GDTs without giving chance for them to react.
.

 

Just be mindful of the following: there is a lot more to a DMM's input protection than the parts themselves. Not only the routing matters (I have seen fuses in series with the voltage jack, for example) but, depending on the nature of the event, a transient may go right through protection devices such as MOVs and GDTs without giving chance for them to react.
.

There's many variables when it comes to input protection and meter robustness but the fact a vendor implemented more than a 2 cent glass fuse says alot about that manufacturer. Transients and Spikes are by there very nature highly unpredictable so by having input protection even at the most basic level it is a definate step in the right direction as far as safety implementation is concerned.

 

There's many variables when it comes to input protection and meter robustness but the fact a vendor implemented more than a 2 cent glass fuse says alot about that manufacturer. Transients and Spikes are by there very nature highly unpredictable so by having input protection even at the most basic level it is a definate step in the right direction as far as safety implementation is concerned.

No question this is a step in the right direction, but it is a very different thing to assume it has decent input protection. My reply references that last statement.

 

No question this is a step in the right direction, but it is a very different thing to assume it has decent input protection. My reply references that last statement.

I'm not assuming anything
It's ETL/INTERTEK Certified so the mfr is adhering to more than the usual CE aka BS protection schema/model. Impressive for a 10$ DMM.

 

I'm not assuming anything
It's ETL/INTERTEK Certified so the mfr is adhering to more than the usual CE aka BS protection schema/model. Impressive for a 10$ DMM.

Ok, that is new information. Thanks for sharing.
What meter is this? Would you mind sharing the manufacturer and model number? I don't see in this post.

 

Ok, that is new information. Thanks for sharing.
What meter is this? Would you mind sharing the manufacturer and model number? I don't see in this post.

The meter is a Mastercraft 052-0060-2, its a rebadged version of the all-SUN EM382B (OEM).