Understanding Premium Class and Standard Class Q-RPT Specifications

On products such as a PPC4 or RPM4 we offer Standard and Premium Class specification for many ranges. There is also a Full Scale Standard Class but it is used rarely so will not include it in the below discussions. It is often difficult to understand how these two classes are different and/or how to interpret the given specification to use in the "real world". Will discuss a couple different ways of stating the same specification as well as how to "visualize" these numbers and run through some actual calculations to hopefully understand these specifications better. The Premium Class specifications are highly dependent on if the AutoRange feature is being used and what value it is set to, so this topic will also be discussed.

To start, here are the two basic specifications:

• Standard Class = .01% of Reading or .0030% of Span, whichever is greater
• Premium Class = .008% of Reading or .0024% of AutoRanged Span or .0007% of Span, whichever is greater

If the above Standard Class specifications make sense to you but are just confused by the Premium Class spec, here is another way to state it and hopefully add some clarity:

• Premium Class = .008% Reading or .0024% of Span, whichever is greater. If the AutoRange feature is additionally being used it allows you to "down range" the Span of the sensor for further measurement improvement. The sensor can be ranged down to as low as 30% of its maximum Span. As an example, a 100 PSI premium sensor can be down ranged to as low as 30 PSI Span and the same .008% Reading or .0024% of the new 30 PSI Span, whichever is greater would then apply. This is a best case example as usually the AutoRange value is set to the value of the maximum pressure of the device being tested.

If neither of the above make sense, here is another way to state the same basic specifications that might make it easier to understand:

• Standard class = .01% of Reading down to 30% of the Span. All pressures below the 30% point are thus fixed at .01% x the pressure value which is at 30% of its Span. In other words it is .01% Reading with a 30% floor. To related this back to the basic specifications, .01% x 30% = the .0030% of Span value shown above. 
• Premium class (if not using AutoRange feature) = .008% Reading down to 30% of the Span. All pressures below the 30% point thus are fixed at .008% x the pressure value which is at 30% of its Span. In other words, it is .008% Reading with a 30% floor. To related this back to the basic specifications, .008% x 30% = the .0024% of AutoRange Span value shown above.
• Premium class (when using AutoRange feature) = .008% Reading down to 9% of the Span. All pressures lower then the 9% point are thus fixed at .008% x the pressure value which is at 9% of its Span. In other words, it is .008% Reading with a 9% floor.
  • • • • • Note, the maximum amount the Span can be AutoRanged down to in terms of measurement specification improvement calculations is 30% of Span. The AutoRange can still be setup lower then the 30% of Span value to set upper limits, etc. appropriately.
            • • • •   To understand how the 9% of Span/floor value was obtained, it is 30% x 30%. In other words, it is the normal floor level of 30% you get on a standard class sensor with the additional 30% down ranging that can obtained with Premium Class using the AutoRange feature.
          • To relate these values relate back to the basic specifications, .008% x 9% = the .0007% of Span value (rounding was used) shown above.
          • The 9% value is a best case scenario so you must keep in mind the actual floor value is dependent on what the AutoRange value is set to. This is usually set to the maximum pressure of the device being tested. So in many cases you will not get the 9% value and it could be anywhere from 9% to 30 of the Span.   

Here is a graphic which often makes understanding these specifications easier. You will notice the Premium Class represented by different shades of green illustrates how it can be "down ranged" to provide maximum measurement specification improvement which will be describe further below:

Since the "AutoRange" feature is in general available on both Standard and Premium Class sensors, but only provides measurement specification improvements on Premium Class, a deeper understanding of this feature is needed:

• The AutoRange Span value is usually set to the value of the maximum pressure of the device being tested.
• The AutoRange has to be manually setup from the front panel of the instrument or defined within software being used
• Standard Class usage
  • • • The AutoRange feature in general can still be used on Standard Class sensors but it does not provide any improvements on measurement specifications.
      • It does provides benefits such as setting an upper limit on the pressure value to help protect the device under test, adjusts the display resolution, and changes control parameters when applicable. 
• Premium Class usage
  • • • Only on Premium Class does it provide improvements on measurement specifications and also provides the benefits such as setting an upper limit on the pressure value to help protect the device under test, adjusts the display resolution, and changes control parameters when applicable.
      • The improvements on measurement specifications or obtained by an additional intense low level characterization on the sensor that allows them to be "down ranged". In other words, it allows say a 100 PSI Span sensor to become say a 30 PSI Span as the low level coefficients are changed in the AutoRange process to allow it to measure more ideally for the reduced range.
      • You must verify AutoRange is actually being used by the operator/software if claiming the full premium class sensor specifications that are related to AutoRange Span. 
        • • • If not using AutoRange on a Premium class sensor it would thus typically be on its default range for that sensor. Would still get the .008% reading component but the full spec becomes .008% of Reading or .0024% of full sensor Span, whichever is greater.
              • • • You can see this illustrated in the graphic above as the darkest green line. 
      • It is very important to keep in mind that the AutoRange value selected ultimately determines what your floor value is. Say you have a 100 PSI Span reference sensor testing a 50 PSI device. You would normally select 50 PSI for your AutoRange. You would thus get a floor spec value of 50 x 30% = 15 PSI. This would then mean you get .008% Reading from 50 PSI down to 15% and all pressures lower then this would remain a fixed measurement spec of 15 x .008%.
      • As also mentioned earlier, the maximum amount the Span can be AutoRanged down to in terms of measurement specification improvement calculations is 30% of Span. The AutoRange can still be setup lower then the 30% of Span value to set upper limits, etc. appropriately. For example, if you have the same 100 PSI Span sensor you get measurement improvements when setting the AutoRange value anywhere from 99 PSI down to 30 PSI. Below 30 PSI there is no further improvements in the measurement spec but if the device you are testing is say 10 PSI maximum pressure it is still advised to use AutoRange to help protect that device.
      • To change the AutoRange value the system must be vented. So, in typical testing this value is set once and used for the entire testing of that device. In other words, you can't keep changing the AutoRange setting as pressures get lower to try and further down range the sensor to improve the measurement specification.
      • The multiple shades of green lines in the graphic above represents three different ranges that can be obtained on a Premium Class sensor
        • • • The darkest green line is the default range without AutoRange being used. If you compare it to the blue line of Standard Class you will see how get the improved .008% Reading spec, but it has the same 30% floor spec as Standard class
            • The medium shade green line example is using AutoRange with it set to a value that is 50% of the total span of the sensor. You can see the sensor thus becomes down ranged and still has the same .008% Reading spec, but it then goes down to 15%. This makes sense because 50% x the standard 30% floor value = 15%
            • The lightest shade green line example is using AutoRange with it set to a value that is 30% of the total span of the sensor. You can see the sensor thus becomes down ranged and still has the same .008% Reading spec, but it then goes down to 9%. This makes sense because 30% x the standard 30% floor value = 9%

Lets now run through some actual calculations of these specifications. To keep the math easy, lets say it is a 100 PSI Q-RPT reference sensor we are using in all the below examples:  

• Standard Class calculations
  • • • The 30% point on the 100 PSI Span sensor would be 30 PSI. So, we thus get the .01% Reading component from 100 PSI down to 30 PSI. All pressures below this remain fixed at the same value as the 30 PSI value. 
        • • • • Lets say our current pressure is 50 PSI. We would thus get 50 x .01% = +- .005 PSI
              • Lets say our current pressure is 30 PSI. We would thus get 30 x .01% = +- .003 PSI
              • Lets say our current pressure is 10 PSI. We would thus be below the 30% point of the sensor so there are no improvements then what we got at the 30 PSI point so would still be +- .003 PSI
              • Lets say our current pressure is 5 PSI.  We would thus be below the 30% point of the sensor so there are no improvements then what we got at the 30 PSI point so would still be +- .003 PSI
              • Lets say our current pressure is 1 PSI. We would thus be below the 30% point of the sensor so there are no improvements then what we got at the 30 PSI point so would still be +- .003 PSI
• Premium Class calculations (if not using AutoRange feature)
  
  • • • Since not using AutoRange the same 30% floor applies and we do not get the additional 30% down ranging. The 30% point on the 100 PSI Span sensor would be 30 PSI. So, we thus get the premium .008% Reading component from 100 PSI down to 30 PSI. All pressures below this remain fixed at the same value as the 30 PSI value. 
        • • • • Lets say our current pressure is 50 PSI. We would thus get 50 x .008% = +- .0040 PSI
              • Lets say our current pressure is 30 PSI. We would thus get 30 x .008% = +- .0024  PSI
              • Lets say our current pressure is 10 PSI. We would thus be below the 30% point of the sensor so there are no improvements then what we got at the 30 PSI point so would still be +- .00024 PSI
              • Lets say our current pressure is 5 PSI.  We would thus be below the 30% point of the sensor so there are no improvements then what we got at the 30 PSI point so would still be +- .00024 PSI
              • Lets say our current pressure is 1 PSI. We would thus be below the 30% point of the sensor so there are no improvements then what we got at the 30 PSI point so would still be +- .00024 PSI
• Premium Class calculations (when using AutoRange feature)
  
  • • • Since using AutoRange we get the additional 30% down ranging and the same 30% floor. If take the 30% x 30% this means our maximum achievable floor for measurement calculations is 9% of Span. The 9% point on the 100 PSI Span sensor would be 9 PSI. So, we can thus get the .01% Reading component from 100 PSI down to 9 PSI in a best case scenario.
      • It is very important to remember how AutoRange works and that usually the AutoRange value selected matches the maximum pressure of the device being tested. This value ultimately determines what your floor spec is, so in many cases you wont get down to the maximum achievable floor of 9%.    
        • • • • Lets say our device being tested is 50 PSI maximum so we set our AutoRange to 50 PSI. The 50 PSI is greater then 30% the Span of the sensor so this is a fully valid AutoRange and we would get the premium .008% Reading component down to 30% of this value. We thus get .008% Reading from 50 PSI down to 15 PSI. All pressures below this remain fixed at the same value as the 15 PSI value. 
                • • • • Lets say Our current pressure is 50 PSI. We would thus get 50 x .008% = +- .0040 PSI
                      • Lets say our current pressure is 30 PSI. We would thus get 30 x .008% = +- .0024 PSI
                      • Lets say our current pressure is 10 PSI. We would thus be below the new 15 PSI floor point of the AutoRange so there are no improvements then what we would get at 15 PSI. We would thus get 15 x .008% = +- .0012 PSI
                      • Lets say our current pressure is 5 PSI. We would thus be below the new 15 PSI floor point of the AutoRange so there are no improvements then what we would get at 15 PSI. We would thus get 15 x .008% = +- .0012 PSI
                      • Lets say our current pressure is 1 PSI. We would thus be below the new 15 PSI floor point of the AutoRange so there are no improvements then what we would get at 15 PSI. We would thus get 15 x .008% = +- .0012 PSI

• • • • • • • • To show the best case scenario that allows us to take the most advantage of AutoRange, lets say our device being tested is 30 PSI maximum so we set our AutoRange to 30 PSI. The 30 PSI is at the 30% the Span of the sensor so this is a fully valid AutoRange and we would get the premium .008% Reading component down to 30% of this value. We thus get .008% Reading from 30 PSI down to 9 PSI which is also the maximum 9% floor mentioned in the specifications discussed previously. All pressures below this remain fixed at the same value as the 9 PSI value.
                
                • • • • Lets say our current pressure is 30 PSI. We would thus get 30 x .008% = +- .0024 PSI
                      • Lets say our current pressure is 10 PSI. We would thus get 10 x .008% = +- .0008 PSI
                      • Lets say our current pressure is 5 PSI. We would thus be below the new 9 PSI floor point of the AutoRange so there are no improvements then what we would get at 9 PSI. We would thus get 9 x .008% = +- .0007 PSI
                      • Lets say our current pressure is 1 PSI. We would thus be below the new 9 PSI floor point of the AutoRange so there are no improvements then what we would get at 9 PSI. We would thus get 9 x .008% = +- .0007 PSI
            • If compare the final +- values in each of the above sets of data it becomes clear the benefit of using Premium Class sensors along with the AutoRange feature. Since the AutoRange feature allows you to down range the sensor the improvements are realized at lower pressures. This ultimately allows one reference sensor to cover a much wider pressure range at the same % Reading spec.