Hameg HM 8122 User Manual Download Page 19

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HM8122 19

Control Panel HM8122

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Power On/St.By

This is a secondary power switch. In the out (St.By) position, power is
supplied only to the oven stabilising circuit of the oscillator.

9 digit display

(7 segment LEDs, 10.9 mm high)

for the measuring result and for digital readout of: measuring time,
exponential notation, constants for RPM, error messages, calibration
informations and indication of “Stand by”. The “Stand By”-mode is
indicated by two vertical segments, lit at the leftmost digit of the
display.

Remote

The remote-LED is lit when the instrument is operated via the IEEE-488
bus. Return to local by pushing the local-switch is possible, provided
the instrument is not in local lockout state.

External Reference

(LED)

This LED is lit when an external reference frequency is applied to the
rear input

Gate Time

(Setting and reading)

The gate time is adjustable from 1ms to 10sec in steps of 1ms, 10ms,
100ms and 1sec. (depending on value) by means of the gate time
potentiometer. The “Read” - switch enables to read the selected gate
time on the display (LED “Read” is lit). When the RPM-function is
selected in read-mode the display shows the number of preselected
pulses per revolution. Gate-time setting is possible either by depressing
the “Read”-switch or during measurements. Gate time setting is not
possible in totalize function and external gate mode.

Gate

(LED)

The gate indicator is lit when the gate is open for measurements. This
time equals the preselected gate time and a synchronisation time. The
gate cannot be open for a time smaller than 1 period of a signal.

External Gate / External Arming

When this control is in the GATE EXT position, the counter will expect
an external control signal, and will not measure until such a signal is
supplied. If it is set to ARM EXT the counter will measure on an active
transition from low to high of the EXT. signal.

Function indicators

LEDs

(Refer to “Measuring functions”)

Function

The “left” and “right” push buttons select the desired function. The
appropriate LED is lit when a function is selected. The default value
when switching power on is Frequency A.

OFL

(Overflow)

This LED is lit when an overflow occurs. This depends on the selected
gate time and of the frequency of the signal applied.

Hz:

Indicates the measurement of a frequency.

Sec:

Indicates the measurement of time.

Reset

Stops a measurement and clears the display in normal measurement
mode. When depressing the button in “Display Hold”-mode the
counter performs a single measurement (one shot) on release of the
button. When the “Offset”-mode is activated, depressing RESET
shows the reference value (which is the actual offset). Reset is active
as long as the button is depressed.

Offset

The displayed value becomes the reference value. (Not available with
the TOTALIZE function).

Display Hold

Depressing the DISPLAY HOLD pushbutton sets the display time to
infinity and freezes the last measurement result. A new measurement
can be initiated using the reset pushbutton or an external reset.
Measuring will restart when

Display Hold

is switched off.

Display

Hold

starts and stops counting in TOTALIZE function mode.

B/C/A

input channels

DC/AC - Low Pass 50kHz - Slope

Input controls

Attenuation 1:10

Input signal attenuators

Trigger Level

(Refer to section “Operation”)

Auto Trigger (AC)

With Auto Trigger active the counter measures the positive and
negative peak value of the input signal and triggers to the 50% value.
Auto Trigger should always be used with AC-coupling.

Common

Connects channels A and B internally. This decreases the input
impedance to 500 k

Ω

. The input control elements of both channels

remain active.

External Reference Input

BNC-socket for connection of an external 10 MHz reference frequency.

External Reset Input

BNC-socket for an externel reset signal (TTL level), equivalent to the
front panel RESET control.

Signal A (B) Output

BNC-socket for trigger signal output channel A (B). Allows the trigger
levels of channel A (B) to be observed with an oscilloscope. Note that
input attenuation of the signals is disregarded, and that the output
trigger level range is limited to 0V...5V.

Gate View Output

A monitor output to allow observation of the measured time interval.
This output is active (high) when the gate is open . It shows the actual
measurement time and is specially useful with time interval
measurements.

External Arming / External Gate Input

Allows the measurment of the input signal, controlled by an external
source.

IEEE bus interface

(Option HO88).