Fluke 35040 Setting Thresholds, Predicted Timed Charge and Dose, Accumulated Charge and Dose

Theory of Operation	2
Basic Operating Equations

Q1 represents the next sample of charge at time T1 following the activation of the timer. Q2 corresponds to the interpolated charge at time T2, where T2 is an integral number of seconds that is restricted to times within the range: T1 < T2 ≤ (T1 + Timer Interval Setting).

Predicted Timed Charge and Dose

This measurement extrapolates the timed charge (QTimed) at the elapsed time (TElapsed) that should be accumulated at completion of the timer interval (i.e., TimerIntervalSetting) based on the rate of charge delivery.

= QTimed[C] ×

QTimed_Predicted TElapsed[s] TimerIntervalSetting[s]

DoseTimed_Predicted = QTimed_Predicted [C] × ICCF [Units/C] × ADCF

At the conclusion of the timer interval (i.e., TElapsed equals the TimerIntervalSetting), the predicted timed charge and dose are equal to the predicted timed charge and dose, respectively.

Accumulated Charge and Dose

This measurement accumulates charge across multiple exposures. The displayed value is updated during the exposure and held between exposures. It is reset to zero when the RESET/MEASURE button is pressed while viewing a measurement screen.

QAccum = QAccum_previous [C] + QExposure [C]

DoseAccum = QAccum [C] × ICCF [Units/C] × ADCF

Exposure Current and Rate

The current (3-1/2 digit) and dose rate displayed when the exposure is in progress are updated once per second. The current and dose rate return to zero after the end of the exposure. The dose rate measurement is displayed using the selected time base (seconds, minutes, or hours). If the start and stop thresholds are set to zero, ILeakage is zero.

IExposure = I [A] − ILeakage [A]

DoseRate = IExposure [A] × ICCF [Units/C] × ADCF × RateMultiplier [s]

Average Current and Rate

The average current is calculated using the charge accumulated ( Q/Ut) during a portion of the exposure to eliminate noise effects. The displayed value (4-/1/2 digit) is held following the exposure and reset at the

⎛	Q2 [C] − Q1 [C]	⎞
IAvg = ⎜		⎟
	T 2 [s] − T1[s]
⎝⎜		⎠⎟

DoseRateAvg = IAvg [A] × ICCF [Units/C] × ADCF × RateMultiplier [s]

start of a subsequent exposure.

Q1 and Q2 are measured within the exposure at times T1 and T2 respectively. T1 is 1.33 seconds after the start of exposure. T2 is 1.33 seconds before the end of exposure (see Figure 2-3). The exposure must be more than 3 seconds long. IAvg is 0 if the exposure is less than 3 seconds.

2.3.1 Setting Thresholds

The instrument has capability to automatically detect the start and end of an exposure when the current crosses given limits. Using automatic detection eliminates the sag in readings that occur due to leakage

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