HM8123 - measurement of pause time / reverse pulses

Question

I need to measure "negative" pulses ( pause time of a signal) using the "Width A" function of the HM8123.
Unfortunately this did not work as expected all the time.

The off time will only be measured correctly after at least one pulse has been detected (which is then not recognized with the correct length in most cases). As my setup's preparation is very elaborate, the first pulse ideally already must give the correct time.
Is there another way to capture the off time? See also attached scope screen shot of the signal (5V High / 0,7V Low):

Answer

1.) "Width A"
This function has some disadvantages for this measurement task. For example it has an uncertainty of 0,4% (1MHz, square wave). Let's assume the HM8123 is already prepared for the measurement and the signal is fed in later on.

The setup after Factory Init of the instrument is the following:
- [Width A]
- CH-A [SLOPE] (set to negative slope, Key will be highlighted)

When now the signal path is switched through, it might lead to wrong measurements as this change of the input level is already detected by the instrument. This can lead to

• misdetection of the first pause or
• wrong measurements factoring in the time between the "start time" (when the signal was applied) and the first pulse

One way for correct usage of the "Width A" function is to prepare the instrument after the signal is already connected to INPUT A. It also helps, to reset the trigger state by just pressing [Width A] again after the signal is applied to the instrument.

2.) "TI A-->B"

This is a much better way to acquire the off time as both trigger events can be defined separately. This function measures the time from trigger point A to trigger point B.
Both INPUT A and B must be applied with the same signal. The setup after Factory Init of the instrument is the following:

- [TI A-->B]
- CH-A [SLOPE] (set to negative slope, Key will be highlighted)

It is possible to add trigger points and filter settings with the keys [LP 50kHz], [DC], [LEVEL A], [LEVEL B], [AUTO TRIG].