Campbell Scientific CR10 CR10 Measurement and Control - Page 186

SECTION 13. CRlO MEASUREMENTS Calculating the actual resistance of a sensor which is one of the legs of a resistive bridge usually requires the use of one or two Processing Instructions in addition to the bridge measurement instruction. Instruction 59 takes a value, X, in a specified input location and computes the value M)U(1-X), where M is the multiplier and stores the result in the original location. Instruction 42 computes the reciprocal of a value in an input location. Table 13.5-2 the instructions used to compute the resistance any single resistor shown in the diagrams in Figure 13.5-1, provided the values of the other resistors in the bridge circuit are known. Instr. 4 TABLE 13.5-2. Calculating Resistance Values from Bridge Measurement Result Instr.# Multiplier; X = Vx(Rs/(R.+R)) XNx Rr=Rf 1-W* 41Nx0 59 Rf 1 Rf= ((x^/xy(1-x /x))/Rs 4 1N* o 59 1/Rs 42 5 X = Rs/(Rs+Rr) X R.=Rt 1_X 5 1 59 Rf 1 Rf= ()u(1-x)yRs 6,8,9* X = 1000 [R./(R3+Ra)-nrl(R1+R2)) R1 = (x1/(1-x1))/R2 where Xr = -)V1000 + R3/(R3+Ra) Rz = Rr(Xzl(1-Xz)) where Xz=Xl Rs = R+(Xs/(1-Xd) where Xs = )(/1000 + R21(R1+R2) R4= (x4l(1-x4))/R3 where X+ = Xg 7&9* X = Rs/Rr Rs = RfX Rt = R.D( 5 1 59 1/Rs 42 *used lor full bridge 6or9 8 6,8, or 9 59 42 -0.001; 1ff* 1tRz R./(R3+Ra) 6or9 59 6or9 59 6or9 59 42 -0.001 Rl 0.001 R4 0.001 1/R3 R./(R3+Ra) Rrl(R1+R2) R2l(R1+R2) 'used as half bridge 7 or9 Rf 0 9 7 or 1/Rs 0 42