I've just obtained a ALCRON ACROMETER 60 DC 30 V / 3 A panelmeter and have some problems calibrating it.
I plan to use it in a home-made bench power supply and the supply's range is 2.75 V to 35 V. The meter has a zero centering screw and using it I managed to set the meter to precisely display the voltage (compared to my other two digital multimeters, which show the voltage to be within 30 mV from each other). This works fine until I set the power supply voltage to around 28 V. At that point, as the panelmeter nears the edge of its range, it starts to show lower voltage. Once the meter reaches end of its scale at 30 V, my multimeters show voltage to be 31 V. If I set it to correctly show 30 V, it shows incorrect value at lower voltages.
Since this is my fist time working with analogue voltmeters, my question is: Is such behavior normal and expected?
The most obvious answer would be to check the manufacturer's web site for datasheets but I was unable to find the site. The only interesting thing written on the box (if my German is good) says that the meter is pre-wired for two 6 V lightbulbs.
Best Answer
Could be an issue with flat vs. upright mounting.
When the needle is too far towards the center at values close to the ends of the scale, the needle of an instrument intended for an upright mounting position might lack the gravity that puts it down just enough to yield a good reading.
When the needle is too far away from the center at values close to the ends of the scale, the needle of an instrument intended for a flat mounting position might be pulled down too far by the gravity that should not act in the direction of the needle's rotation.
Usually, little symbols indicate the specified mounting position, e.g. an upside-down T means you are to use the meter upright, and a table-like symbol similar to \$\sqcap\$ means the instrument must be used in a horizontal position.
Examples may be found in this link. (Sorry German only, but you will certainly understand vertikal and horizontal.)