1, 4, 5, 6 – Gearing, 2,3 – pointers, 7,8 – eddy current units.

This scheme differs from the scheme of one-pointer indicator in presence of specific gearing 1, 4, 6, and 5. By means of this gearing the two pointers 2 and 3 move from their drag-type units 7 and 8 each. Friction in the gearing reduces pointers oscillations, appearing at transient processes. That is why in two-pointer (dual) indicator on fig.5, b, the drag-type damping unit is not used (in contrast to the one-pointer indicator fig.5, a).

A bbbb

Fig.5

The main errors appear in tachometer as a result of change of moving element electric resistance, induction in the air-gap, characteristics of constant magnets, and the construction parameters of sensitive element, linear dimensions of counteractive spring and absolute value of its material resilience because of the environment temperature. The moving element is made with small temperature coefficient. Other temperature changes are compensated in the device by means of temperature shunt 6 (fig.1), fastened on the constant magnets 5. The main instrumental errors of tachometer are determined by friction in bearings of moving units and scale calibration errors, which are equal to 1%. Tachometer ITE - 2 (electric tachometric instrument) differs from ITE – 1 by the fact, that it has two pickups such as PTE (electric tachometric pickup). These pickups are connected with their engine shaft and appropriate sensitive element each. Both measuring units are assembled in one case and have combined axis of pointers indicator (fig.5, b). As the gear couples are used for transmission of moving element rotation angle to the pointer axis, and there is friction in these gear couples, promoting quick attenuation of the moving systems, so there are no dampers in measuring units of the concerned indicators.

The most typical malfunctions in tachometer operation are demagnetization of measuring unit magnets and faulty phase connection of the pickup and indicator.

The main technical characteristics

The indicator scale is divided from 0 to 105 % and digitized from 0 to 100 %.

Minimum scale value of tachometer is equal to 10 % by its scale. The indicator scale is equidistant, scaling factor is 1 %.

Scale working range is 60% – 100%.

In surrounding air temperature +20±5°С, +50±5°С, -60±5°С tachometer’s errors shouldn’t exceed the following values:

Table 1.

Measuring limit, rpm. in %%	Errors in %% of tachometer sets at temperatures
	+20±5°С	+50±5°С	-60±5°С
10-60 exclusive	±1,0	±1,5	±2,5
60-100 inclusive	±0,5	±1,0	±1,5
100-105	±1,0	±1,5	±2,5

The measuring device works surely at vibration overload 1,1 g in frequency range from 10 to 80 Hz. At the same time displacement of the pointers shouldn’t exceed 1 mm along the scale arc, and oscillation amplitude of the pointer is to be less then 1 mm.

The pickup can stand vibration overload 10 g in frequency range from 10 to 200 Hz.

The terminal voltage between each two phases of pickup PTE-2, loaded with two motors of the measuring device (ITE-1 or ITE-2), or pickup PTE-1, loaded with one motor of the measuring device (ITE-1 or ITE-2), at 60% by the device scale (1500 rpm of the pickup rotor) should be within the limits from 10 to 12,5 V after device continuous work during one minute.

The temperature range of pickups operation is from -60±5°С to 180±5°С. (Continuous work of pickups is allowed at +150°С during not more than 15 hours, and at 180°С – not more than 5 hours).