User manual
Appendix
ComTec GmbH 7-14
The 'Move' button moves the ADC from the 'Coincident with any' group into the dependent group, it is
removed from the 'Coincident with any' group, whereas the 'Copy' copies it into the dependent group and
lets it in the 'Coincident with any' group. Using 'Copy' and 'Move' it is possible to have an ADC in several
dependent groups and remove it from the 'coincident with any' group. It makes no sense to have any
ADC as well in the 'coinc. with any' as in a dependent group, because any event is registered already if
this ADC has a valid conversion because it is in the 'coinc. with any' group, no matter whether it is in a
dependent group or not.
Q: Please let us know what we should do to carry out anti-coincidence measurement by using MPA-3.
A: An event can be rejected with a TTL signal. It makes no sense to reject by a converted ADC signal
because one should not measure the amplitude of a signal and then reject this information because it
causes dead time. You can either use the gate input of the ADC's or you could use the reject input, the
3rd auxiliary connector at the MPA-3 base module:
Press in the Coincidence definition dialog the button "Aux conn..". The Auxiliary connectors dialog is
opened. For the REJECT input enable the checkbox "Coincidence Mode", define the input signal polarity
and use "Instantly" reject (or reject "at end of coincdence" window). Close the Auxiliary connectors dialog
and you have now /REJ in the "Coinc. with any" list. You can use it for the coincidence groups like an
ADC, for example move it into a dependent group. Note that for positive polarity the signal at the REJ
input must have a rising edge within the coincidence time window or for negative polarity a falling edge.
To make an anticoincidence, you can also define spectra with a condition set on a ROI. Define a ROI
containing a complete ADC spectra, define a condition for events NOT inside that ROI, and set this
condition on any other spectra you want to gate with this anticoincidence.
Q: I know in the MPA2 system if the DEAD signals do not arrive within the coincidence window then a
zero is returned. Is this also the case with the MPA3 system?
A: No. In the MPA-3 the zero is returned when a Dead time signal was present but no Data Ready did
come within the data-ready-timeout. It means that either this timeout was too short or the pulse was
below the threshold. In the MPA/PC-II a zero was returned in "coincidence mode" also when no signal at
all was present. In the MPA-3 only data from ADC's are stored that had a Dead time signal (for singles
only the Data Ready is observed). For each event an information word informs which ADC's had fired.
Q: A related question for another customer: On the MPA-3, this customer proposes to capture 16
parameters, consisting of 8 pairs (X-Y). He wants to know if coincidences can be set up for these 8
groups of 2 parameters each. In looking at the software, it seems there is a maximum of 4 groups that
can be defined (set up)? Is it possible to specify 8 groups, each consisting of 2 parameters?
A: It is in principle no problem to expand the software up to 8 dependent coincidence groups. If
necessary, we can make this software expansion without any additional cost. Of course the customer
could also use all ADCs in the 'Coincidence with any' list and is then free to see any coincidences. The
data flow is not higher when there are always events in pairs of two ADC's, because for any coincidence
event always an informational word is transfered saying which ADCs had data and then only the data
words of ADCs are transfered that performed a valid conversion (this is very different from the data flow in
the old MPA/PC-II system).
Q: I need some more explanation about setting the coincidences. If an ADC1A (with S) is entered into the
"Coincidence with any" column of the dialog box, is this equivalent to: (for example)??? "Accept an event
as valid if it occurs on ADC1A and any other ADC that is shown as active within the coincidence window
time setting? ie. ADC1A and (ADC1B OR ACD1C OR......) ??? It is intended as just a short format to
state this same logic? What would occur if the START box was not checked, so there is no "S" after the
ADC1A? The discussion of this in the MPA-3 manual is very brief.
A: The Start enable means that this ADC is allowed to start a coincidence window. If it is not checked, it
cannot initiate storing an event and it is stored only if its Dead time signal is within the coincidence
window started by any other ADC with the Start enable attribute. If ADC1A with S is entered in the
"Coincidence with any" column, it is equivalent to: "Accept an event as valid if it occurs on ADC1A and
start a coincidence window. Store then the converted value of ADC1A and of any other ADCs that had a
dead time signal within the coincidence window". It is not possible to decide which of the ADC's started
the coincidence window if more than one in an event have the S attribute. If no other ADC had a dead
time signal within the coincidence window, this single value is stored alone.