How to use the MF-47 Pointer Multimeter to measure full bias current
Pointer multimeters as a whole have different full bias currents at different stops. If you want to measure the full bias current of the meter head alone, you need to disconnect the meter head from the circuit. The following is a description of each.
①Meter full bias current
MF47 multimeter has a lot of gears, all DC voltage gear full bias current is 50μA, so the current gear in the 50μA position, is the base of the table gear, this gear problem other gear accuracy will not be able to talk about.
Measurement of full bias current should be based on 50μA.
Test voltage E = 1.5 ⅴ, current limiting resistor R = 18 ~ 22KΩ, potentiometer W = 10KΩ, fullness current Ⅰ = 50μA, the instrument internal resistance r = 5KΩ. Turn on the circuit and slowly rotate the potentiometer to the fullness of the pointer to the fullness of the position, this time the digital meter display is the "full bias current" value.
To measure the full bias current of other current gears, the same method as above, but need to reduce the resistance value of R. The resistance value of R can be based on E/l = R + r (other current gear internal resistance r were 500mA ≈ 1Ω, 50mA ≈ 6Ω, 0.5mA ≈ 540Ω) to count 萛, in order to give W a margin for adjustment, the value of R take 70% to 80% can be. In general, do not omit the R, or once the potentiometer in the zero Ω position, it is possible to break the meter.
②Table head full bias current
MF47 head sensitivity of 46.2μA, in access to the multimeter circuit, the head is connected in parallel with a lot of shunt resistors, so that the head part of the overall sensitivity of exactly 50μA, the internal resistance is also enough to make up 5KΩ.
Measurement of the instrument to open the back cover, at least disconnect the head of a lead, the head and shunt resistor implementation of the separation, and then according to the above picture of the way to measure it alone.
In addition to shunt resistance in parallel on the head of the meter to provide damping, once disconnected, the loss of damping the needle needs to swing a number of times to stop, which is a normal phenomenon.
