Can we do function check for vibration switch Model as VS94 Frank W. Murphy.

Is there any procedure available to calibrate or functional check.
Is there a facility, instrument, equipment, etc helps to do functional check.

 

A Google search for "VS94 Vibration Switch" yielded this:

http://www.fwmurphy.co.uk/products/vib_time_speed/vibration_switch_vs94.htm

Clicking on the 'Installation Instructions' link halfway down the page yielded:

http://www.fwmurphy.com/uploaded/documents/pdfs/00-02-0185.pdf

The typical "adjustment" for this switch is to keep adjusting it until it doesn't "trip" when the motor or device it is monitoring is started, then turn the adjustor another 1/4 turn. The only way to really test them is to rap them with a rubber mallet, or to "un"-turn the adjustor until the switch "trips" when the motor/device is started.

Devices like this provide very basic, and adequate, protection when properly installed and maintained.

But, there is no way to really calibrate them to any repeatable specification (at least that I have ever seen or employed). I imagine someone could make or buy something, but the cost compared to the cost of these switches would be pretty high.

 

Dear CSA

thank you for your replay, but i understand that we are not able to know the existing set point of the trip.

if we turn it till it trip how can we re-adjust it again.

note in my case it used for big fans with 3 meters blade, we are not allowed to touch the switch unless the fan if isolated (off).

 

This type of switch is commonly used for this same type of application. The switch is a very "crude" device, but very adequate for the application. It's primarily intended to provide an indication or to stop the motor driving the fan blades if there is some large imbalance in the fan, such as if a blade is damaged, or broken or not secured properly (becomes loose).

The switches in these applications are adjusted so that the "bump" that occurs when the fans are started by induction motors does not "trip" the switch, and then, as the instruction sheet says, another quarter-turn is taken to provide a slight "deadband" in the adjustment. Some times the fans are driven by motors through gear-drive mechanisms which can transmit a large bump when the induction motors are first started. Other fans are belt-driven so some of the bumping from induction motor starting is lessened, but if the switches are not properly "adjusted" they can still be actuated by the starting bump.

There is no calibrated setting for these types of switches, they are crude but adequate switches meant to detect large imbalances in rotation. I would venture that no two switches at your site on this equipment being protected with these switches are adjusted exactly the same. It's just virtually impossible to do so. Look at how they're constructed: magnets and metal and screws and air gaps. You would need be able to measure magnetic strength across the air gap to be able to calibrate, or duplicate settings.

You can count the number of turns (or partial turns) that you have to turn the switch until it is "tripped" by the bump of the induction motor when being started, and then return it to that setting (which should, theoretically, be approximately one quarter turn!). But, again, these are not, nor for these types of applications do they need to be, sensitive devices with precise calibration setpoints which can be measured or duplicated. Just read the instructions provided by the manufacturer for these switches. About the most sophisticated part of them is a remote reset feature.

If you want more information about the settings of these switches on the fans at your site, you should contact the supplier of the module or equipment that has the fans. They should be able to tell you how they intended the switches to be adjusted for proper operation if you have "doubts" (how I loathe that word!) about the switch manufacturer's instructions. Have you looked at the instruction manual(s) provided by the equipment manufacturer? There may be (usually is) some information like this for switches and instruments in the instruction manuals produced by the manufacturer and provided with modules/equipment.