Digital Analog Tech Note 03 - TNDA03

Abstract

This document describes the behavior of Counter C including how (A-B) and (A+B) describes the counter's action but is not a mathematical function.

Products

PAXC & PAXI Counters

Problem Description

When counter C is used to display the sum or difference of counters A & B in the PAXI or PAXC rate/counter meters, the formula C = A – B, or C = A + B is only true if counters A and B have not been reset or all counters (A,B, & C) have been reset simultaneously. When only one or two of the three counters (A,B, & C) are reset, counter C represents an accumulation of counter A & B inputs only and not the true sum or difference of their displayed values.

The PAXI and PAXC literature, PAXC - X, PAXI – X, and PAXICR – X, are misleading when describing the operation of Counter C. The description of Sub Ab states “Counter C counts the incoming pulses from Counter A and B inputs as per Counter A and B modes of operation and subtracts the B counts from the A counts.” However, If both A & B counters are programmed for Count X 1, and counter C is programmed for “Sub Ab” an input to counter A will cause 1 to be added to the value of counter C and an input to counter B will cause a 1 to be subtracted to the value of counter C. If counter C is programmed for “Add Ab”, an input to either the A or B counters will cause 1 to be added to the value of counter C. This is the function of the C counter regardless of the displayed values of counters A & B. If at anytime these counters are reset individually, The value in Counter C will no longer represent the sum or difference of Counter A & B displayed values.

Example 1

Counter C is programmed to Sub Ab (C = A – B). After all three counters are reset to 0 the following sequence is true:

(A)10 – (B)5 = (C)5
(A)10 – (B)6 = (C)4
(A)10 – (B)7 = (C)3

If counters A & B were reset at this point in the sequence, the sequence will continue as follows:

(A)0 – (B)0 = (C)3
(A)1 – (B)0 = (C)4
(A)2 – (B)0 = (C)5
(A)2 – (B)1 = (C)4
(A)2 – (B)2 = (C)3
(A)2– (B)12 = (C)-7

Example 2

Counter C is programmed to Add Ab (C = A + B) After all three counters are reset to 0 the following sequence is true:

(A)1 + (B)0 = (C)1
(A)1 + (B)1 = (C)2
(A)1 + (B)2 = (C)3

If counters A & B were reset at this point in the sequence, the sequence will continue as follows:

(A)0 + (B)0 = (C)3
(A)1 + (B)0 = (C)4
(A)2 + (B)0 = (C)5
(A)2 + (B)1 = (C)6
(A)2 + (B)2 = (C)7
(A)2 + (B)12 = (C)17

Example 3

Counter C is programmed to Add Ab (C = A + B) After all three counters are reset to 0 the following sequence is true:

(A)1 + (B)0 = (C)1
(A)1 + (B)1 = (C)2
(A)1 + (B)2 = (C)3

If counter B is reset and counters A and C are not, the sequence would continue as follows:

(A)1 + (B)0 = (C)3
(A)1 + (B)1 = (C)4
(A)1 + (B)2 = (C)5
(A)2 + (B)2 = (C)6
(A)3 + (B)2 = (C)7
(A)3 + (B)12 = (C)17

Example 4

Counter C is programmed to Sub Ab (C = A - B) After all three counters are reset to 0 the following sequence is true:

(A)1 - (B)0 = (C)1
(A)1 - (B)1 = (C)0
(A)2 - (B)1 = (C)1

If counter B is reset and counters A and C are not, the sequence would continue as follows:

(A)2 - (B)0 = (C)1
(A)2 - (B)1 = (C)0
(A)3 - (B)1 = (C)1
(A)3 - (B)2 = (C)0
(A)3 - (B)3 = (C)-1
(A)6 + (B)3 = (C)2

Disclaimer

It is the customer's responsibility to review the advice provided herein and its applicability to the system. Red Lion makes no representation about specific knowledge of the customer's system or the specific performance of the system. Red Lion is not responsible for any damage to equipment or connected systems. The use of this document is at your own risk. Red Lion standard product warranty applies.

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