How is the ICE-PIC used as verification on 1720 series turbidimeters?

Document ID

Document ID TE6754

Version

Version 2.0

Status

Status Published

Published Date

Published Date 27/05/2017
Question
How is the ICE-PIC used as verification on 1720 series turbidimeters?
Summary
ICE-PIC verification use for 1720 series turbidimeters.
Answer
Use of the ICE-PIC with the 1720E:
In this explanation we will focus on the 1.0 NTU device. The same arithmetic applies to all versions.
  1. ICE-PIC calibration units are sold with a nominal value. The 1.0 NTU ICE-PIC can be 1.0 NTU +/- 25%. i.e. 0.75 NTU - 1.25 NTU. This explains the 25% statement in the instructions.
  2. The actual value of the turbidity of the ICE-PIC must be established (assigned) by the user, immediately following a full calibration/verification of a 1720E (EPA 90-day cycle). This assigned turbidity value is specific to that 1720E.  That same ICE-PIC may be assigned a simultaneously valid different value of turbidity when used with a different 1720E following a similar calibration on that instrument. These (minor) different turbidity values are not relevant; however gross differences (e.g. 5% of nominal value) should raise concern.
  3. The ICE-PIC may only be used for verifications between the EPA specified 90-day calibration/verifications.
  4. The +/- 10% referred to for ICE-PIC verifications refers to +/- 10% of the assigned value on that specific 1720E as detailed in sub paragraph 2 above.
Example - Assignment of actual value to an ICE-PIC
The single ICE-PIC delivered nominal value – 1 NTU, as supplied by Hach.
 “Instrument A” and “Instrument B” are different 1720E turbidimeters.
The actual value assigned to the ICE-PIC by “Instrument A” following a Primary Calibration/Verification of “Instrument A” is 0.92 NTU.
The actual value assigned to the ICE-PIC  by “Instrument B” following a Primary Calibration/Verification of “Instrument B” is 0.87 NTU.
Both of these assigned values are between 0.75 NTU - 1.25 NTU (+/-25%) which is this acceptable range specified by Hach for the ICE-PIC. These values will be recorded in the respective Calibration/Verification logs of the two instruments. 
Example of Verifications using the ICE-PIC
A subsequent (e.g. weekly) Verification of “Instrument A” yields 0.98 NTU.
Determination of Verification Pass/Fail for “Instrument A”
100 * (0.98 – 0.92)/0.92 = 6.521%.   This is a Pass for “Instrument A” as the percentage difference is less than 10%.
 
A subsequent (e.g. weekly) Verification of “Instrument B” yields 0.7 NTU.
Determination of Verification Pass/Fail for “Instrument B”
100 * (0.75 – 0.87)/0.87 = -13.793%.   This is a Fail for “Instrument B” as the percentage difference is more than 10%. Corrective action is required.