User Guide - Eurotherm Ltda

nanodac RECORDER/CONTROLLER: USER GUIDE3.4.10 Steriliser Display Mode (Cont.)F 0F 0 is a means of calculating ‘equivalent time at sterilising temperature’ for temperatures below, at and abovesterilizing temperature, using the equation below.F0= Sterilisation time×10Temp−TsZWhere:Sterilisation time Depends on the application, typically 15 minutes at Ts = 121°CTempThe value of the temperature measuring input.TsDesired Sterilising temperatureZ Temperature interval representing a factor-of-10 reduction in killing efficiency. Z = 10for steam sterilising (F 0 ), or Z=20 for dry heat sterilising (FH). Z = 10 for thermal disinfection(A 0 ).To ensure that steriliser loads which contain materials with different thermal inertias are thoroughly sterilised,a number of sensors are located withing the load. The F value should be calculated using the sensorclosest to that part of the load which has the highest thermal inertia. For maximum accuracy, the temperaturesensor should be calibrated and the input adjust function used to compensate for any inaccuracy found.F0 calculation examplesFor all the examples following, the following are assumed: Sterilisation time = 15 minutes; Sterilisation targettemperature =121°C and Z = 10.1. For an actual sterilising temperature of 111°CFval = 15 × 10111 10 -121= 15×10-10 10= 1.5minutesWhich means that 15 minutes at 111°C is equivalent to 1.5 minutes at 121°C2. For a sterilising temperature of 121°CFval = 15 × 1010 -121= 15×1010 0=121 15minutesWhich means that the sterilising temperature is ideal (by definition)3. For a sterilising temperature of 124°CFval = 15 × 10124 10 -121= 15×1010 3= 15×1.995 = 29.925minutesWhich means that 15 minutes at 124°C is equivalent to nearly 30 minutes at 121°C.Normally sterilising temperatures would not remain constant at temperatures below or above the target value,so the above equations are illustrative only of the facts:1 Temperatures below the target have some killing efficacy2 Temperatures above the target value have a greater killing efficiency, so that the sterilising time can bereduced.In order to calculate the value dynamically, the instrument uses the equation:ma t -Target tempFvalt = Fvalt-1+ T × 10ZwhereFval t = F value this iterationFval t-1 = F value last timeT = Iteration period (minutes)ma t = input temperature value this iterationTarget Temp = 121°C for F 0 , 170°C for F H , 80°C for A 0Z = 10°C for F 0 , 20C for F H , 10°C for A 0HA030554Issue 7 Nov 12Page 43