RPM indicator 4 to 20mA signal some time frozen.

Thread Starter

aung Htut

Joined Feb 8, 2023
1
I have some issued of RPM analog meter(4 to 20mA) was some time frozen and i had swapped from working RPM indicator then working satisfactory however some time rpm meter was some time frozen.What is the problem issued? RPM indicator or 4 to 20mA signal.
Thgank
 

Jerry-Hat-Trick

Joined Aug 31, 2022
544
A 4 to 20mA analog meter is probably moving coil with the return spring adjusted so that the pointer doesn't move off zero until at least 4mA flows. To test the meter still functions you could take maybe a 9V battery and connect in series with the meter and a 1.0k ohm resistor. The actual resistance of the meter will probably be quite small so a 1k ohm resistor should move the needle about one third of full scale
 

KeithWalker

Joined Jul 10, 2017
3,063
Is this an electro-mechanical meter movement? If so there are several things that could cause it to stick.
Worn bearings can cause the meter movement to tip, causing the pointer to touch the scale.
Magnetic debris in the meter or dried lubrication in the bearings.can cause it to stick.
Overlapping coils in a damaged hairspring can cause it to stick.
etc, etc.
You will probably have to open it up and take a look.
 

strantor

Joined Oct 3, 2010
6,782
Are you opening the meter? Most of these meters are unsealed; you can open them, remove the scale behind the needle, and insert a custom scale, even a hand drawn one, with the units and graduations that you want. It is fine (and intended) to do this, but you absolutely must do it in a clean environment, using clean tools. Any kind of seemingly insignificant debris that gets inside can mess up the meter. Especially if it is metallic. The meter movement is magnetic and will attract metallic particles. Are there tiny bits of metal stuck to the end of your magnetized screwdriver? If so, they will somehow find their way into the meter movement immediately after you open the meter face, and they will cause issues like you described.
 

Flashy

Joined Jun 7, 2010
4
I have some issued of RPM analog meter(4 to 20mA) was some time frozen and i had swapped from working RPM indicator then working satisfactory however some time rpm meter was some time frozen.What is the problem issued? RPM indicator or 4 to 20mA signal.
Thgank
If you are using a moving coil meter the magnets may be affected by the cold this is dependant on the quality of the magnetic material and the temperature change it goes through. This is the curie temperature and varies with the magnetic material. Cheaper instruments will be affected mostly. check any Data sheets.
 

MisterBill2

Joined Jan 23, 2018
18,167
I have had a problem with the needle sticking to the glass because of static electricity, and the simple fix is a good brand of anti-static spray. Never had to open the meter or get involved with the wiring. About $230 cheaper than the replacement meter another person claimed was needed.
 
Top