Subject: [OPSAWG] pmPowerAccuracy in claise-energy-monitoring-mib-03

From: "Juergen Quittek" <[email-masked]>
Date: Wed, 19 May 2010 07:08:25 +0200

Dear all,

It's great to have an update of this MIB module proposal.

I look forward to a vivid discussion as preparation for 
the merger of draft-claise-energy-monitoring-mib and 
draft-quittek-power-mib.

I have a set of comments that I will send in separate emails
in the next days. Here comes the first one. 
It's on managed object pmPowerAccuracy:

     pmPowerAccuracy OBJECT-TYPE 
         SYNTAX          Integer32 (0..10000) 
         UNITS           "hundredths of percent" 
         MAX-ACCESS      read-only 
         STATUS          current 
         DESCRIPTION 
            "This object indicates a percentage value in 100ths of a 
            percent representing the accuracy to which the usage, 
            reported by the pmPower can be assumed. Example 1010 
            means the reported usage is accurate to +/- 10.1 percent.  
            This value is zero if the accuracy is unknown or not 
            applicable based upon the measurement method. 
                
            ANSI and IEC define the following accuracy classes for 
            power measurement: 
                 IEC 62053-22  60044-1 class 0.1, 0.2, 0.5, 1  3. 
                 ANSI C12.20 class 0.2, 0.5" 
         ::= { pmEntry 15 } 

I don't see how this would work. It is correct that the standards
referred to specify the accuracy of a meter in percent. However,
It is percent of the maximum value that can be reported by the meter.
Where would I get this maximum value from? 
It's not specified in the MIB.

Hence, the value of this object is useless
because I do not know how much the actual power value 
may differ from the reported one.

In draft draft-quittek-power-mib-01 we specified the maximum error
value instead of the percentage value. The maximum error is the product 
of the percentage value and the maximum value that can be reported by 
the meter:

   energyConsumpEnergyMaxError OBJECT-TYPE
       SYNTAX      EnergySensorMaxError
       MAX-ACCESS  read-only
       STATUS      current
       DESCRIPTION
           "This object indicates maximal error of the measured energy
           consumption values provided by objects
           energyConsumpTotalEnergy and energyConsumpPSTotalEnergy.

           The actual value of the consumed energy may be greater or
           less than the reported value with the maximal difference
           between actual and reported value indicated by this object.

           A value of 0 indicates that the maximum error is unknown."
       ::= { energyConsumpEntry 7 }

TC EnergySensorMaxError is defined for Values reported by objects of
type EntitySensorValue. It can be modified in case we decide not to 
use the EntitySensor MIB module.

    Juergen