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Input Conditioning Controls
- Controls the citcuitry that converts the input into rectangular waveforms (analog to digital).
- Accomplished using Schmiti Trigger.
Coupling control has two positions AC & DC.
-In the AC position a capacitor is in series with the input thus limiting lower frequencies / DC. Primarily for symmetrical waveforms or signal riding on a DC reference.
-In the DC position the signal is directly couped. Allows the windest possible bandwidth to pass. Used for non-sysmmetrical or very low frequencies.
Provides a continuous adjustment of the DC level where triggering occurs within the hysteresis windows.
Reduces the signal amplitude thereby increasing the range of the input signal.
The attenuators will decrease the signal and noise by the same factor.
- Determines whether the counter will trigger on the leading edge or trailing edge.
INPUT IMPEDANCE CONTROL
Input impedance is used to match the output circuit of the equipment being measured.
Matching the imapedances reduces the loading effect and allows maximum power to be transferred. It also cleans up the signal providing better fidelity.
Used for removing undesired frequencies from the signal.
-Primary function of an electronic counter.
-This reference is a TBO or time base oscillator.
-TBO and the time base dividers determine how long the main gate is open.
-Display will read in hertz.
-Period is simply the inverse of frequency.
-In period function the input signal now determines how long the gate is open.
-Pulses from the TBO are now counted and the arithmetic section computation will display in seconds.
Period of time display in seconds.
TIME INTERVAL FUNCTION / TIME INTERVAL MODE
- Used to measure the time between two events.
- Input ch.A & ch.B determine the output of the main gate which opens & closes.
TIME INTERVAL DELAY (Sub-Function)
Causes an inhibit stop for a specific time (delay) allowing measurement between serial data pulses.
Measure between two events
PULSE WIDTH (Sub-Function)
Sets counter level for 50% points of the input waveform.
RISE/FALL TIME (Sub-Function)
Sets start and stop at 10% and 90% levels of the input waveform.
Averaging may be done during time interval or period operation. Only needs two pulses.
-Reduces +/- one count ambiguity error thus increasing accuracy.
Used to display the ratio between two frequencies.
- Compares the TBO with itself.
- It's a functional check only and is not a valid measurment.
GATE TIME CONTROL
Controls the time base dividers to allow gating of the main gate. This ensures the gate will be open long enough to obtain a measurment.
- Has 3 states.
- 1. If the indicator is flashing a trigger is being produced.
2. If the triggering level is higher than the input signal the indicator will be illumunated.
3. If the triggering level is lower than the input signal the indicator will be off.
The gate indicator will illuminate when the counter circuitry is allowing a signal to pass.
- Causes for no gate are:
- - Improper trigger level adjustment.
- - Input signal amplitude is too low.
- - Sample rate set to hold.
- - External gate selected on the rear with no external gate applied.
- Arm indicator indicates the counter is ready to make a measurment.
- (Arm And Ready)
- Overflow Indicator shifts the Most Significant Digit (MSD) to the left and out of view.
- Underflow Indicator shifts the Least Significant Digit (LSD) to the right and out of view.
TIME BASE ERROR
Caused by the crystal-controlled oscillator being off frequency.
+/- 1 COUNT AMBIGUITY ERROR
An inherent +/- 1 count error in the least significant digit.
Error exists because the main control gate is not triggered by or synchronized to the input signal being counted.
Random error caused by noise.
- Cause by user setup.
- -Is caused by slight variation between both input channels will cause inaccurate counts.
- -Only relevant when using both channels at the same time.
THE TIME BASE
- Standard use for comparison.
- It must be accurate and it must maintain this accuracy over a period of time.
- Frequency Accuracy- expressed in a +/- value.
- Frequency Stability- The ability to maintain a set frequency over a period of time.
POWER SUPPLY TEST
Consult the manufacturer's manual.
Built in diagnostics test.
Ensure all display segments and annunciators illuminate.
Measures the minimum signal amplitude that will produce a stable count.
POWER SUPPLY ADJUSTMENT
- Recheck all supply voltages after making an adjustment.
- Power supply adjustments should always be performed prior to any further measurements.
- Consist of many adjustments: Slope, Trigger, Attenuator, and Bais adjustment.
- Impedance must be matched and attenuation should be minimum.
TIME BASE OSCILLATOR (TBO) ADJUSTMENTS
Ensure that the time base oscillator and oven have had sufficient warm up time.