U52: reading OTP values (not used in Phyaction Guidance E/C).
Microcontroller guard
component (U 64):
Amplitude generation circuits
: U14 produces a DC signal in relation to the demanded intensity. The
output signal of U14 is the reference value for U24 that produces the amplitude modulated (AM)
signals for the LF currents (MF, DF, CP, LP, IF).
The output signals are connected to the signal processing circuits.
5.1.3 Safety control circuits.
The main goal of the safety circuit is to protect the patient and the Electrotherapy circuit from too
high currents.
In case of an error, the safety relay is switched off and a error code is generated.
A special safety controller (U36: PIC16C74) monitors and controls all the safety components used in
the Guidance E/C.
/ Note that even when an error is not longer occurring, the output state of the RS flipflop stays ‘low’
and the safety relay remains off. The unit must be restarted in order to continue any treatment.
The following items are constantly checked:
Measured current in relation to the set intensity:
Comparator U1 and DAC U25 guard the output level. U1 compares the output signals from the
current measuring circuit (CUR_A SAF/CUR_B SAF) with the reference voltages
(FDBACK_SAFA/FDBACK_SAFB). These reference voltages are generated by the safety DAC
U25 and are setup by the microprocessor U36.
In case of a problem, the PROTECTION signal will go ‘LOW’ and the safety relay is switched off.
The limit values are different for each current waveform plus they depend on the set intensity level.
The safety controller sets the limit for each current waveform via the AD converter U 25.
Proper functioning of both the microcontrollers:
If the PIC microcontroller detects a problem with the Siemens microcontroller, it will switch off the
safety relay by making the MC_SRY_off signal ‘high’ (microcontroller safety relay off).
If, on the other hand, the Siemens microcontroller detects a problem with the PIC, it will switch off
the safety relay by making the S_SRY_off signal ‘high’ (Siemens safety relay off).
VCC:
In case the VCC (5V) goes below 4.75 V, an error is generated via the POR line which causes the
safety relay to switch off.
Rotary channel A and B:
The value of the encoders (= intensity knob) are measured by the PIC and compared by the Siemens
microcontroller.
Phyaction Guidance E/C – service manual version 0.5 Page 16
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