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Supervision of Sine Cosine Encoders

Sine / Cosine Amplitude Comparison

The measurements have been made with a 2048 period single turn encoder

speed (rpm) S400/600 S300/S700
0 100 % 100 %
1000 96 % 98 %
2000 91 % 89 %
3000 85 % 77 %
3500 80 % 70 %
4000 76 % 64 %
4500 72 % 58 %
5000 69 % 52 %
5500 64 % 47 %
6000 61 % 42 %
6300 58 % 40 %

Supervision with S400 and S600

The default supervision supervises in the supervision IDLE the sum of sin² and cos² for minimum and maximum values at about every 1ms. The summarized signal of sin² and cos² is evaluated by a low pass filter with a time constant of 16ms.

Minimum :
sin² + cos² > (3000Inc)²
=> 1 Vss ≡ 10813 Inc
=> from 1 Vpp • 3000 / 10813 = 0.277 Vpp the feedback error F04 appears.
This voltage value is still not critical, because the digital comparator, that operates the sine and cosine signals, works up to a voltage level of 0.122 Vpp (same as with S300 and S700).

Maximum :
sin² + cos² < (16380Inc)²
=> 1 Vpp ≡ 10813 Inc
=> from 1 Vpp • 16380 / 10813 = 1.5151 Vpp the feedback error F04 appears
This voltage level results from the maximum resolution of the AD converter (5 V / 3.3 V).

Additional supervision from Firmware version 6.24

From FW 6.24 there is a second, parallel supervision, that can be switched on with DRVCNFG bit 30 (0x40000000). With this supervision, the sum of the absolute values of sine and cosine signals are compared with limit values, in the the 250µs task of the amplifier.

sincos_ueberwachung.jpg

In the figure the principle behavior of the sum signal (yellow) of absolute values of sine and cosine signals with 1 Vpp sine and cosine signals.

Minimum:
From FW versions 6.24 up to 6.35 the minimal value of the sum signal is supervised with:
| sin | + | cos | > 5000 Inc
The sum signal becomes minimal, if the signal crosses zero, with a resolution of 0.5 Vp ≡ 5406 Inc this results in:
=> 5000 Inc ≡ 0.462 Vp
=> 5000 Inc ≡ 0.925 Vpp
If the value falls below this limit, the feedback error F04 occurs.

From FW version 6.37 the minimal value of the sum signal is supervised with:
| sin | + | cos | > 2700 Inc
The sum signal becomes minimal, if the signal crosses zero, with a resolution of 0.5 Vp ≡ 5406 Inc this results in:
=> 2700 Inc ≡ 0.25 Vp
=> 2700 Inc ≡ 0.5 Vpp
If the value falls below this limit, the feedback error F04 occurs.

Maximum :
The maximum value of the sum signal is supervised with:
| sin | + | cos | < 11200 Inc
The sum signal becomes maximal, if both signals reach 1/√2 = 0.707 of their maximum amplitude (see figure). With 0.5 Vp this is the sum signal 0.707 Vp:
=> 11200 Inc / √2 ≡ 7919 Inc
The value 7919 refers to the amplitude of sine and cosine signals, with a resolution of 0.5 Vs ≡ 5406 Inc this results in:
=> 7919 Inc • 0.5 Vs / 5406 Inc = 0.732 Vp
=> 1.46 Vpp
If the value rises above this limit, the feedback error F04 occurs.

Supervision with S300 and S700

S300 and S700 use the same supervision method as S400/S600. The sum signal of sin² and cos² is evaluated via a low pass filter with a time constant of 16ms.

Minimum:
As minimum value a signal is supervised from FW 0.71, that is equivalent to an input signal of 0.2 Vpp. Because the AD converter signal is not factorized with 4 (see "Resolution processing of Sine Cosine Encoders"), this is equivalent to an incremental value of 270 inc. If the value falls below this limit, the feedback fault F04 occurs. The evaluation operates in the 62.5µs task of the amplifier.

Maximum:
As maximum value a sum signal is supervised, that is equivalent to an input signal of 1.46 Vpp. Because the AD converter signal is not factorized with 4 (see "Resolution processing of Sine Cosine Encoders"), this is equivalent to an incremental value of 1971 inc. If the value rises above this limit, the feedback error F04 occurs.