» High Voltage Voltmeter (0775)

Immagini

DESCRIPTION

Exhibit 775 is a high voltage electrostatic voltmeter of the type Starke-Schroder. The apparatus consists of two large metal disks fixed to two vertical isolated columns. The columns are mounted on a horizontal metal base on which is also attached a support for a lamp and a graduated scale (see design-1).

One of the disks is fixed. The other disk is movable and has in its center a small window that supports a small steel strip soldered to a wire (2) and a mirror (3) with two rocker arms. Each disk supports a terminal for the external electrical connection.

The wire serves as a torsional spring. The distance (S) between the disks can be varied. See photo 2 and 3.

Upon applying an elettrostatic voltage (Vt) between the two disks, an attractive force (Ft) appears betweeen them, the mirror rotates and reflects the light beam to a position on the scale calibrated in units for a standard separation of the disks.

The disks behave as a parallel plate condenser with the separation x variable. If the capacity of this condenser is C and the applied voltage is Vt, then the accumulated energy is:

The variation is:

Equazione: [dE= \frac{1}{2}V^2_t dC= F_tdx]

Thus the force has the value:

Equazione: [F_t= \frac{1}{2}V^2_t \frac{dC}{dx}]

For a condenser $Formula: [C=\frac{A\epsilon}{x}]$ , thus $Formula: [\frac{dC}{dx}=-\frac{A\epsilon}{x^2}]$ Then

Equazione: [F_t=-A\epsilon\frac{V^2_t}{x^2}]

where A is the area of each disk and ε the dielectric constant (ε = 1 for air). One deduces that the attractive force between the disks is proportional to the square of the potential difference and inversely proportional to the square of the distance between the disks. The unit intervals on the scale are proportional to the square of the standard voltage. That is, the attractive force rotates the mirror which reflects the light beam through units proportional to the square of the voltage for the standard separation S.

For further details see ref.1.

ISCRIZIONI

Su un piede è posta una targhetta: "Dipl. Jng R. SCHROEDER¶
Fabrik elektrischer Messapparate¶
Aache, Junkerstra{\ss}e 93¶
Hochspannungsvoltm Nr.A W 172¶
D.R.P.u. Ausl. P. angem.¶
Für 80KV GL W"
Su un piede è posta una targhetta: "ING. S. BELOTTI & C.¶
MILANO¶
PIAZZA TRENTO"

BIBLIOGRAPHY

[1] Kind Dieter; Feser Kurt, "High Voltage Test Techniques", Newnes, 2001. Pag. 21.

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