Feasibility study of in-house second-channel calibration of dual-channel electrometers using a battery-powered current source.

Figures

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  FIGURE 1. Conceptual diagram of this research model. Step 1: Pass a current through the reference electrometer for 60 s and calculate the current value and t ref. t ref is the calibration point in a standard laboratory; details are shown in Table 2. Step 2: Pass a current through t ref to the reference electrometer and measure its sensitivity. Step 3: Pass a current through t ref to the EUT and measure its sensitivity. Calculate the sensitivity ratio from the two measurement results.

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  FIGURE 2. Conceptual diagram of method A. The sensitivity of first‐circuit of the RAMTEC Pro electrometer is used as the reference. Electrometer sensitivity coefficient k elec,user is measured using second‐circuit of RAMTEC Pro and first‐circuit and second‐circuit of both RAMTEC Duo and SuperMAX as EUTs.

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  FIGURE 3. Conceptual diagram of method B. The sensitivity of first‐circuit of every electrometer is used as the reference to determine sensitivity coefficient k elec,user for second‐circuit. This method has a radiotherapy facility that possesses only one dual‐circuit electrometer and uses first‐circuit of the same unit as the internal reference.

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  FIGURE 4. Detailed formula for calculating k elec,user using Method A. Method A uses kelecPro,#1 because it is based on the first circuit of the RAMTEC Pro.

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  FIGURE 5. Detailed formulas for calculating k elec,user using method B. Method B uses a different k elec because it is based on the first circuit of each EUT.

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  FIGURE 6. Relationship between the electrometers used in this study and the differences between k elec and k elec,user. Electrometers are labeled according to the circuit they are based on and method A or B. For example, “RAMTEC Pro_#2_B” indicates the second‐circuit of RAMTEC Pro, method B (Figures 3 and 5).