This page shows you how to modify the MU45-QP5014 panel meter (0-5A) into other useful meters. Covered here are 0-50mA, 0-500mA, 0-50mV, 0-500mV, 0-5V and 0-50V.
In the pictures and text below, we modify the 5A meter into a 50mA meter.
This is the starting point - the unmodified meter. Start by turning it over and note where the front and body meets:
You can remove the front by a firm, but careful, pressure on one of the corners.
Remove the two screws indicated in the picture above and carefully slide the scale out without damaging the needle of the meter. If you are careful, it is very easy to do this right.
Place the scale (we'll need it again), screws and front in a safe place - we're going to work on the body internals.
The wire indicated by arrow "1" in the picture is the shunt resistor for the amperes meter. Note that the actual meter at "2" has been placed in a safe position, so we can work on the internals without damaging the needle. Use a small cutting tool to remove the shunt.
In the picture above, the shunt has been removed. Now we move on to make the new scale. Download the scale wanted (in this example, we use the 50mA scale) and print it out. Adjust the size of the printout to match the size of the original scale (it's 2.0" x 1.25" or 5.1x3.2 cm.).
Using some universal glue, glue the new scale on top of the old - if you glue the new one on the back side, you can reverse the operation later. After the glue is dry, slide the new scale in place and assemble the meter again.
Finally, we need to mount the external resistors to make the correct scale. In this case we mount a pair of 1.5Ω and 2.2Ω resistors in parallel as shown in the picture below.
Current: 16.7 mA
50mA - use shunt resistor (place over terminals) of 0.895Ω (e.g. 1.5Ω in parallel with 2.2Ω = 0.892 or less than 1% error).
500mA - use shunt resistor (place over terminals) of 0.062Ω. To obtain this resistor, try with a piece of wire of different length and use a potentiometer, a multimeter and a battery all connected in series (including the panel meter) and adjsut the length of the wire until 500mA on the multimeter equals 500 mA on the scale on the panel meter.
50mV - simply remove the existing shunt and the panel meter is a 50mV meter - no external resistors is needed.
500mV - use a 27Ω resistor in series with the meter.
5V - use a 300Ω (150+150) resistor in series with the meter.
50V - use a 3027Ω (1k5+1k5+27) resistor in series with the meter.
Start by downloading the empty scale: null.jpg
When placing the numbers on the scale, use the "Arial Narrow 28p" font and for the text use "Arial 28p". The number should be placed at angels (from left to right) -37, -25, -9, +9, +25 and +37 degrees.
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