43B
Service Manual
3-4
The Input 1 and Input 2 measurement circuits are partially identical. The differences are:
• Only Input 1 provides facilities for Ohms, Continuity, Diode, and Capacitance
measurements.
• The bandwidth of the Input 1 circuit is 20 MHz, the bandwidth of Input 2 is 15 kHz.
• Input 2 has an additional hum rejection circuit.
The circuit description below applies to the Input 1 and Input 2 circuit.
Input 1 and Input 2 measurement principle
An input voltage applied to Input 1 or Input 2 is supplied to the C-ASIC via the HF path
(Input 1 only) and the LF path. Depending on the actual measurement function the
Input-1 HF path in the C-ASIC is enabled or disabled. The HF DECade ATTenuator and
LF DECade ATTenuator are external components for the HF and LF path. The C-ASIC
converts (attenuates, amplifies) the input signal to a normalized output voltage
ADC-A/ADC-B, which is supplied to the Analog to Digital Converters (ADC-A and
ADC-B) on the DIGITAL part. The D-ASIC acquires the digital samples to build the
traces, and to calculate readings.
For the electrical functions the current Input 2 circuit is operating in low voltage ranges.
For example a current of 10A measured with a 1 mV/A current clamp generates 10 mV
(voltage range 10 mV/div). To minimize the influence of interference voltages, Input 2
has no HF path, and has an additional hum reject circuit.
The lowest Input 1 voltage range for electrical measurements is 4V/div, which is high in
comparison with the Input 2 range.
Ohms, Continuity, and Diode measurement function (Input 1 only)
The T-ASIC supplies a current via the Ω/F relays to the unknown resistance Rx or diode
connected to the Input 1 and the COM input jacket. The voltage drop across Rx or the
diode is measured according to the Input 1 measurement principle.
Capacitance measurement function (Input 1 only)
The T-ASIC supplies a current via the Ω/F relays to the unknown capacitance Cx,
connected to the Input 1 and the COM input jacket. Cx is charged and discharged by this
current. The C-ASIC converts the charging time and the discharging time into a pulse
width signal. This signal is supplied to the T-ASIC via the C-ASIC trigger output
TRIG-A. The T-ASIC shapes and levels the signal, and supplies the resulting pulse
width signal ALLTRIG to the D-ASIC. The D-ASIC counts the pulse width and
calculates the capacitance reading.
Scope measurement function
In the Scope measurements function the test tool shows the traces and readings derived
from the input signals. The Input 1 HF path is enabled, which results in a 20 MHz
bandwidth. The Input 2 bandwidth is 15 kHz.
Other measurement functions
Volts/Amperes/Hertz (LF), Power (LF), Harmonics (LF), Sags & Swells (LF),
Transients, Inrush Current (LF), and Temperature measurement results are calculated
from acquired input voltage samples. For functions with (LF), the HF path of Input 1 is
disabled, which results in a 15 kHz bandwidth for both Input channels.
Miscellaneous
Control of the C-ASIC, e.g. selecting the attenuation factor, is done by the D-ASIC via
the SDAT and SCLK serial communication lines.
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