7.3.4 Peak Detector/Indicators
Schematic 2105-070 sheet 2 & 3.
When the voltage applied to the rear panel terminals exceeds 250% of the selected voltage
range, the peak voltage indicator illuminates. This signals that the displayed voltage and power
value may not be accurate and that spikes may be present on the input signal. An identical
circuit provides a visual signal when the current to the load exceeds 250% of the selected
current range. The peak detectors provide their visual signals irrespective of whether "Amps" or
"Volts" has been selected for display.
The voltage peak detector is composed of comparators U10-1, U10-2 and U10-13. Their circuit
is shown in the upper area of drawing 2105-070 sheet 3. The reference voltage at the inverting
input of U10-6 is at -12 volts, which is derived from the divider composed of R28 and R30. The
non-inverting input is connected to the output of the voltage amplifier, IC1-6. The non-inverting
input U10-5 is at +12 volts which is derived from the divider composed of R24 and R26. Its
inverting input is also connected to the output of U9-6.
When zero volts are applied to the input, the outputs of both comparators are high (+15 volts).
Since the inverting input U10-11 is at ground potential, its output will be high, back-biasing
voltage peak indicator D2 and holding it out of conduction.
When the input voltage (either peak or steady-state) e12 volts, the output of U10-1
will transition to -15 volts, causing the output of U10-13 to transition to -15 volts, turning on
D2. When the input voltage exceeds -12 volts, the output of U10-2 and U10-13 will transition to
-15 volts to turn on D2. An integrating capacitor C18 holds the output of U10-13 at a low state
between peaks so that D2 is continuously illuminated until the input to U10-13 is increased
above its transition level.
An identical circuit for the current peak detector/indicator is composed of U5-1, U5-2, U5-13
and associated components. The input to this detector is from the output of the selected
current signal amplifier.
7.3.5 Analog to Digital Converters
Schematic 2105-070 sheet 6
There are two nearly identical digital voltmeter (DVM) circuits. These are shown on the
schematic 2100-070 sheet 6.
7.3.5.1
Volts/Amps Display
The Analog to Digital conversion in the Model 2105 is allowed by U13 and its associated
components. The reference voltage applied to U13-2 is 1Volts. 1.2Volts are generated by D9
and adjusted by RV22. X1 generates a 100 kHz clock signal for U13-22; the frequency of the
oscillator allows the 2105 a conversion rate of 3 readings per second. The digital portion of U13
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