The Moisture Meter of Grain for Drying Control (I)

The Factors which influence Detector Current

Abstract

The anther designed a high frequency type electrical moisture meter so as to make possible automatic moisture content controls for the continuous flow grain dryer. Because this meter was too sensitive to variability of grain conditions flowing in the continuous dryer. The meter readings were very scattered. In addition, the kind and the temperature changes of grain could not be neglected. Also the meter readings were affected by the chemical components of parched grain and its bound water in addition to the free moisture of grain. Its equivalent moisture was about 4.2-4.5% of the apparent density of parched grain in the case of unhulled rice. The auther investigated these factors which influenced meter readings systematically and in the detail. The main results were the followings;
1. When the filling method was controlled, the standard deviation of the apparent density of grain in the test cell was reduces to 1/8 of the result of no controlling. Dependence of the apparent density on moisture contents was little observed.
2. The detector current I of the high frequency type electrical moisture meter of the resonance circuit method was formularized as the following to general;
I=I_m0G_t0[G_t²+ω²(C-L/Z²)²]^-1/2 (7)
Where,
G_t=1/R_pc+1/R_px+R_L/R_L²+ω²L²
C=C₁+ΔC₁+C_x
C_x: The electrical capacity of grain.
R_px: The effective parallel resistance of grain.
3. In the case of C-L/Z²>0, the relation between the detector current of the meter developed and the apparent effective moisture density (a tentative name) of grain was formularized as the following;
I=I_m0G_t0/(a+bθ)d_0s⁸+I_m0G_t0X (21)
Where,
d_0s=(w_d+β)d_2e
d_0s: The apparent effective moisture density, βd_2e: The apparent equivalent moisture density (a tentative name) the chemical components of the parched grain and in its bound water, θ: The grain temperature. d_2e: The apparent density of the parched grain, w_d: The moisture ratio (dry base).
4. When the filling method was controlled, the standard deviation of the moisture content (wet base) measured with this meter was reduced to 1/3.8 of the result of no controlling.
5. The relation between the meter reading and the moisture ratio w_d was formularized as the following:
I=I_m0G_t0/(a+bθ)(β+w_d/1+w_dd_1e)⁸+I_m0G_t0X (25)
When the meter readings were corrected by the measurement of the apparent density of grain d_1e, the standard deviation of the moisture content measured with this meter was reduced to 1/5.6 of the result of no correcting.
6. With the described the standard deviations of measurement of the moisture content were 0.29-0.24% in case of the unhulled rice in the tempering. The standard deviations were of deviations between the oven dried standard moisture contents and the ones calculated by equation (25).