D’Arsonval meter base system uses permanent magnets and coils round. Therefore meters D’Arsonval commonly referred to as a Permanent Magnet Moving Coil (PMMC). Shown in Figure 5.6. D’Arsonval needle movement system requires very low power and a small current to the deviation needle on a full scale.
Figure 6.7 Schematic picture PPMC meter (D’Arsonval)
The equation for the torque that causes the needle to move are:
T = B x A x I x N
Where
T = Torque
B = magnetic flux density in Wb / m2
Idp = Current in the coil around in amperes
N = Number of rotary coil windings
Figure 6.7 shows the construction of a basic meter rotary spindle (PPMC) simplified to make it easier to understand the movement of the needle meter mechanization system. In the given rotary shaft coil spring so that the needle gently so that the meter can be reverted to its original position after the current that causes a torque on the coils play does not exist. PPMC measuring tool applied to ampermeter, voltmeter and ohmmeter.
Rotary spindle-based measuring instrument is a precision measuring instrument with high accuracy. The level of accuracy of the measuring instrument is determined by the basic meter specifications PPMC. Characteristics of PPMC important basic meter which determines the class ketelitiannyaadalah:
– Flow meter nominal basis stated in mikroamper or miliamper
– resistance in the meter which is the resistance of the coil rotary expressed in ohms.
Here is given an example the case of a measuring instrument PPMC with the following specifications:
– Koil rotary coil consists of 84 windings, with a length = 1.5 cm, and width coil = 1 cm with a resistance value of Rm = 88 ohms.
– magnetic flux density (B) = 0.2 Tesla (weber / m2)
– nominal allowable current flows through the coil rotary (Idp) = 0.5 mA
– full needle deviation of 100 degrees.
Analysis:
– With the size of the coil which has a length of 1.5 cm and a width of 1 cm, then the coil cross-sectional area (A) was 1.5 cm2 or 1.5 x 10-2 m2.
– With a flux density of 0.2 weber / m2 and the number of coil windings rotary spindle (N) = 100 windings, and the value of the current flowing in the coil of 0.5 mA (miliamper) or 0.5 × 10-3 amperes, the torque value received by the coil rotary spindle (T) according to the torque above formula is:
(0.2 weber / m2) (1.5 × 10-2 m2) (0.5 × 10-3 amperes) (100 loops) = 1.5 × 10-4 Nm (Newtonmeter)
So if the coil is energized rotary direct current of 0.5 mA, will receive a torque of 1.5 × 10-4 Nm. Of torque that will make the needle meter rotary motion. Because mechanization needle is made such that at a current of 0.5 mA, then the needle will be deviated by 100 degrees. As shown in Figure 6.8.
Figure 6.8 The movement of needles due to presence of Torque
PPMC basic meter is not calibrated to measure certain electrical quantities, for example ampermeter, voltmeter, and ohmmeter commonly known as the galvanometer. Galvanometer is a basic meter with a very small measuring limit is usually of the order of mikroamper. Typically galvanometer has a zero in the middle, as shown in Figure 6.9.
Figure 6.9 Galvanometer