Measurement-computing WaveBook rev.4.0 Manuale Utente Scaricare il pdf (Pagina 56)

4-10 WaveBook Operation Reference

06-08-01

WaveBook User’s Manual

•

Without SSH, the trigger threshold is settable from -5.0 to +9.996 volts with 12-bit

(WaveBook/512) resolution, regardless of any channel's gain settings. This gives better than

1% resolution at even the smallest input ranges (such as 0-1 or ±0.5 volts).

•

With SSH, the single-channel (Channel 1 analog) signal is first amplified by the SSH

programmable gain amplifier before being compared with the programmable voltage. This

allows precise trigger-level adjustment, even at high gain. The analog-trigger comparator

threshold-voltage range and resolution (with SSH) are shown in the following table.

SSH Input Range Trigger Threshold Range WaveBook/512

12-Bit Resolution (mV)

WaveBook/516

16-Bit Resolution (mV)

0-10 or ±5 -5.0 to 9.996 3.66 0.299

0-5 or ±2.5 -2.5 to 4.998 1.83 0.114

0-2 or ±1 -1.0 to 1.999 0.732 0.0458

0-1 or ±0.5 -0.5 to 0.9996 0.366 0.0229

0-0.5 or ±0.25 -0.25 to 0.4998 0.183 0.0114

0-0.2 or ±0.1 -0.10 to 0.1999 0.0732 0.00458

0-0.1 or ±0.05 -0.05 to 0.09996 0.0366 0.00229

Hysteresis

The analog trigger circuit has hysteresis that reduces the occurrence of retriggering due to input noise.

The hysteresis level without SSH is 25 mV; the hysteresis with SSH is 1/600 of the comparator range. The

next figure shows the hysteresis effect for a rising-edge trigger.

Trigger

Trigger Level

Hysteresis Range

Hysteresis Effect on a Rising-Edge Trigger

Amplitude

Time

A trigger will occur when the analog input rises above the trigger level—but only after the input level has

been below the hysteresis range. If the level momentarily drops just below the trigger level (perhaps due to

noise) and then rises above it again, no extra triggers will be generated—the signal did not drop below the

hysteresis range. After the level drops below hysteresis, it can then again produce a trigger by rising above

the trigger level.

Multi-Channel Trigger

When the small hardware-limited latencies of the digital (TTL) and single-channel (Channel 1 analog)

triggers are not required, the DSP chip may be used to examine the samples from one or more channels and

to decide if they constitute a pre-defined trigger condition.

The DSP can sample up to 72 input channels and

examine each one to determine if it meets programmed

levels for a valid trigger. This multi-channel triggering

is a two-step process:

The DSP examines each of its specified input

signals to determine trigger validity.

After all of the channels have been examined, the

DSP logically combines the individual triggers to

generate the actual trigger. The DSP may be

programmed to generate a trigger if

any

individual

trigger is valid (OR) or if

all

triggers are valid

(AND). See figure.

rigger

etector

rigger

etector

nalog

nput

ignals

nvalid Trigger

alid Trigger

e-Arm Command

rom Control Circuits

o Trigger

AND

(all)

rigger

(any)

Trigger

Logic

rigger

etector

ulti-Channel Trigger Detection

Trigger validity in a multi-channel environment is determined by the logical relationship among three

elements (

slope, duration

, and

initialization)

as discussed in the next section.

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