User's Manual for CM6G - Yokogawa

6-146.5.3 Correcting ComputationAs this calorimeter sets the differential pressure of both sample gas (∆Pg) and air (∆Pa) to 500 Pa,but, in order to correct the indication error due to the variation of the differential pressure (Flow rate),the correcting computation is practiced.The detection signal is obtained through the measurement with the standard differential pressure of500 Pa, but if each differential pressure change to ∆Pg and ∆Pa (≠500 Pa), the detection signal shallbe changed from Eo to E’o.∆ PgE’o = Eo •(6.1)∆ PaTherefore, if we multiply the detection signal E’ostandard differential pressure.∆Pa / ∆Pg , we can correct to the value at theIn the computing program, each differential pressure is extracted of the square root and providea differential pressure correcting computation. The signal after corrected is range suppressed(ZERO) and to further extended to SPAN. In case when it has a preheat circuit deduct the amountof preheated value and extend to SPAN, then being range suppressed and shall be extended againto SPAN. Further as to generate the output of the calorific signal, the following density correction isnecessary:K = C(WI) • ρg(6.2)Also it is necessary for each signal to operate with a timing matched with the signal of the caloriedetector and for this reason, dynamic characteristic function is provided. (A-CORR. RATE, A-TIME,G-CORR. RATE, G-TIME)Remarks: In case of pre-heating circuit exists, the formula is as follows:K∆ PgH∆θ = C1 • • + C2 •(6.3)ρg∆ Pa∆ PaH : Pre-heat calorieC1, C2 : Constantρg : Density of the gasIf the correction computation of the differential pressure is provided to ∆θ in the formula (6.3), it isshown as per the following formula:∆ PgKH∆θ • = C1 • + C2 •(6.4)∆ Paρ g∆ PgThe second clause of the right part in the formula (6.4) represent the preheat calorie, which, as youcan see in the formula (6.4), the matters concerning the preheating is varied according to the changeof differential pressure (∆Pg).In this computing program, if there is preheating circuit, multiply the constant by the differentialpressure signal, and after correcting the differential pressure to the preheating, the deduction of thepreheat calorie is computed.IM 11R02A01-02E