BK Precision 5105A Instruction Manual download pdf (Page 7)

Subject to change without notice

Type of signal voltage

The following description of the 5105A relates to the

analog-oscilloscope mode. Please note “Storage Opera-

tion”.

The oscilloscope 5105A allows examination of DC vol-

tages and most repetitive signals in the frequency range up

to at least 150MHz (-3dB).

The vertical amplifiers have been designed for minimum

overshoot and therefore permit a true signal display.

The display of sinusoidal signals within the bandwidth limits

causes no problems, but an increasing error in measurement

due to gain reduction must be taken into account when

measuring high frequency signals. This error becomes

noticeable at approx. 70MHz. At approx. 110MHz the redu-

ction is approx. 10% and the real voltage value is 11% higher.

The gain reduction error can not be defined exactly as the -

3dB bandwidth of the amplifiers differ between 150MHz

and 170MHz.

For sine wave signals the -6dB limit is approx. 220MHz.

When examining square or pulse type waveforms, attention

must be paid to the harmonic content of such signals. The

repetition frequency (fundamental frequency) of the signal

must therefore be significantly smaller than the upper limit

frequency of the vertical amplifier.

Displaying composite signals can be difficult, especially if they

contain no repetitive higher amplitude content which can be

used for triggering. This is the case with bursts, for instance.

To obtain a well-triggered display in this case, the assistance

of the variable hold off function or the second time base may

be required. Television video signals are relatively easy to

trigger using the built-in TV-Sync-Separator (TV).

For optional operation as a DC or AC voltage amplifier, each

vertical amplifier input is provided with a DC/AC switch. DC

coupling should only be used with a series-connected atte-

nuator probe or at very low frequencies or if the measure-

ment of the DC voltage content of the signal is absolutely

necessary.

When displaying very low frequency pulses, the flat tops may

be sloping with AC coupling of the vertical amplifier (AC limit

frequency approx. 1.6 Hz for 3dB). In this case, DC operation

is preferred, provided the signal voltage is not superimposed

on a too high DC level. Otherwise a capacitor of adequate

capacitance must be connected to the input of the vertical

amplifier with DC coupling. This capacitor must have a

sufficiently high breakdown voltage rating. DC coupling is

also recommended for the display of logic and pulse signals,

especially if the pulse duty factor changes constantly.

Otherwise the display will move upwards or downwards at

each change. Pure direct voltages can only be measured with

DC coupling.

The input coupling is selectable by the AC/DC pushbutton.

The actual setting is displayed in the readout with the “ = “

symbol for DC- and the “ ~ “ symbol for AC coupling.

Amplitude Measurements

In general electrical engineering, alternating voltage data

normally refers to effective values (rms = root-mean-square

value). However, for signal magnitudes and voltage desi-

gnations in oscilloscope measurements, the peak-to-peak

voltage (V

) value is applied. The latter corresponds to the

real potential difference between the most positive and most

negative points of a signal waveform. If a sinusoidal

waveform, displayed on the oscilloscope screen, is to be

converted into an effective (rms) value, the resulting peak-

to-peak value must be divided by 2x√2 = 2.83. Conversely, it

should be observed that sinusoidal voltages indicated in V

rms

eff

) have 2.83 times the potential difference in V

The relationship between the different voltage magnitudes

can be seen from the following figure.

Voltage values of a sine curve

rms

= effective value; V

= simple peak or crest value;

= peak-to-peak value; V

mom

= momentary value.

The minimum signal voltage which must be applied to the Y

input for a trace of 1div height is 1mV

(± 5%) when this

deflection coefficient is displayed on the screen (readout)

and the vernier is switched off (VAR-LED dark). However,

smaller signals than this may also be displayed. The deflection

coefficients are indicated in mV/div or V/div (peak-to-peak

value).

The magnitude of the applied voltage is ascertained by

multiplying the selected deflection coefficient by the vertical

display height in div. If an attenuator probe x10 is used, a

further multiplication by a factor of 10 is required to ascertain

the correct voltage value.

For exact amplitude measurements, the variable control (VAR)

must be set to its calibrated detent CAL position.

With the variable control activated the deflection sensitivity

can be reduced up to a ratio of 2.5 to 1 (please note “controls

and readout”). Therefore any intermediate value is possible

within the 1-2-5 sequence of the attenuator(s).

With direct connection to the vertical input, signals

up to 400Vpp may be displayed (attenuator set to

20V/div, variable control to 2.5:1).

With the designations

H = display height in div,

U = signal voltage in V

at the vertical input,

D = deflection coefficient in V/div at attenuator switch,

the required value can be calculated from the two given

quantities:

However, these three values are not freely selectable.

They have to be within the following limits (trigger threshold,

accuracy of reading):

H between 0.5 and 8div, if possible 3.2 to 8div,

U between 0.5mV

and 160V

D between 1mV/div and 20V/div in 1-2-5 sequence.

Type of signal voltage

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BK Precision 5105A Instruction Manual Page 7

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