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Saturday, 19 June 2021

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JJ-B Series

Our standard laboratory balance: The readability of up to 300,000 individual measuring steps is our current limit with the DMS technology.

In the versions with 0.01g steps, the scale is delivered with a 170 * 195 mm weighing surface.
The finer versions with 0.001g have a round weighing surface, under a large glass windscreen.

 

Shielding

UIn addition to the substructure made of cast aluminum, under the white upper shell made of impact-resistant plastic, another metal shield several millimeters thick is located around these most important components to filter out interfering radiation.

 

You probably know the effect from your cell phone. When you are calling a person, your call is converted by your phone into an electronic signal. This signal is send as radio waves in all direction, emitted by the antenna of the mobile phone. In a view km distance the signal will reach a transmitting mast of the phones network provider. When the radio wave contacts the antenna of the recieving mask, it will again create an electronic signal, that is then send to the person which is called and there again is converted into a conversation. 

If you now place your phone next to a radio antenna, you will hear the effect that the signal is not just transfered to the mast, but unaimed in all directions. If you are close enough, you will hear loud knocks and beeps. 

Of course, a scale does not have an antenna, but these electrical radiations affect all conductive components, such as cables and sensors, in all electrical appliances.
For most devices, this is not a problem. But inside of a digital scale there is a transmitter, thar normaly should only recieve the measurement signal from a load cell and that has to be extremely sensitive to register minimal changes in the measurement signal when adding tiny amounts during dosations.

In that area, no strong transmittion of e.g. the phones antenna is more required, the scale can already be disturbed by all devices that build an electric field. Especially devices with strong capacitors or motors. In the laboratory, this includes e.g. Centrifuges, shakers, magnetic stirrers or the power supplies of other devices.

 

For scales without shielding, these faults are only filtered out by an sensitivity filter software. The weight that is shown in the display, is only shown with an delay of several seconds and an average weight is formed during this time. If there is a "cracking noise" during this time, you will not see much of it in the display. Vibrations, or other short disturbances such as "background noise" in the radio, are filtered out via a software vibration filter. This also helps against other influences and makes it possible, even on cheap scales, to weigh a switched-on mobile phone in a room with a strong draft on a wobbly table, relatively accurate.

 

Both together only becomes problematic if you do not weigh solid objects but dose them on the balance. The low sensitivity with the averaging computation causes the display to change only slowly, especially with the addition of only small amounts in the display, and the oscillation filter would not display all minimal changes (for example, if 0.998g is over and you want to add 0.002g again). Only after adding more mass does the balance "jump" to a new value, e.g. 1,002g.

 

For all professional scales, we already offer you the option to set the scale to dosing mode and completely deactivate the filters. Now every signal received by the load cell is displayed, as well as every fault.

If you want to add 0,002g again at 0,998g and the scale shows 1,000g in the display, you may have dosed 2mg. Or it may be that you have added 1mg and another mg is displayed because your neighbor gets a call. 

Our series JJ-A and JJ-B have a closed area to shield this radiation as much as possible from the measuring electronics.
Only at the top there is necessarily a small hole through which the load cell is connected to the weighing surface.
This capsule makes up about half of the case. Outside of this are the non-critical systems such as the control of the keyboard or the display. The whole thing is then surrounded by the white ABS housing. Additional, the 0,001g models have the solid wind shield with temped glass mounted on top of this. 


 

Underflorr measurement

Another advantage of the JJ-B series is the simple underfloor measurement, mostly used for density determination. Simply place the scale on our optionally available stable metal stand.
A table with a hole in theplate of course works the same way. Hang the small included hook under the scale below. 


Now P
lace the sample on top of the weighing surface and make a note of the weight.
Example: A piece of gold.
 

Then place the sample in our stainless steel basket, supplied with the optional density determination kit, with several liters capacity and hang the basket in the provided tank, which you can conveniently fill and empty with a hose connection. Optionally, you can of course use a piece of wire, tie the sample on it and let it down into a bucket of water (it must be completely submerged, but without touching the ground of the bucket).
The two results between air-mesurement and submerge measurement you can use for the calculation of the density. 



 

Another example for the underfloor weighing:
Gold is a not magnetic material, unlike other metals with a similar density and you could check the gold coins easily with a strong neodym magnet on the scale. But the problem here also is, that the magnetic force may cause wrong weight results when placed directly on the scale or near it. 

For this, place the scale again on the mount pictured above and hang the magnet on a cord, so you have about 10 mm distance to the ground. If you now place a gold coin on the ground, under the magnet without touching it and the display is showing a heavier weight, the coin may have an in melted core of tungsten or other material. At a coin with pure gold nothing will happen.

 

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