Bias algorithm

The ratio algorithm provides a means by which two strategies can manipulate the same variable. In our example both the feedforward and feedback parts of the scheme can change the flow of stream B as necessary without flghting each other. 

Rather than multiply them together, an alternative means of combining two signals is to add them. In addition to the ratio algorithm, the DCS is likely to include a bias algorithm. This performs in a similar way to the ratio. When in manual mode the bias (B) is determined by 

When switched to automatic this calculation is replaced by 

With the flow of fuel A incorporated as a DV, we can apply the bias algorithm to maintain the total fuel constant. The bias algorithm supports the addition of a scaling factor on its input. In this case we set this factor to — 1. If we think as the output from the temperature controller being the total fuel required, the bias now subtracts the flow of fuel A from this 

As with ratio feedforward, some DCS include the bias as an option within the PID algorithm. Some also permit configuration of the operator display to make the algorithm appear like a true controller with both the actual bias and the bias SP. 

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Second virial coefficients represent the first approximation to the system equation of state. Yethiraj and Hall [148] obtained the compressibility factor, i.e., pV/kgTn, for small stars. They found no significant differences with respect to the linear chains in the pressure vs volume behavior. Escobedo and de Pablo [149] performed simulations in the NPT ensemble (constant pressure) with an extended continuum configurational bias algorithm to determine volumetric properties of small branched chains with a squared-well attractive potential... 

G. Psihoyios, A block implicit advanced step-point (BIAS) algorithm for stiff differential systems, Comput. Lett., 2006, 2(1-2), 51-58. 

Instead of the error (PV- SP) being calculated in the controller it is calculated in each of die two bias algorithms. The two errors are compared in the signal selector and the selected... 

From Chapter 2, we know that (Kp)m varies inversely with feed rate. If we were to configure the output of the bias algorithm to manipulate the fuel flow directly, rather than the fuel-to-feed ratio, then we would need to include adaptive tuning to automatically adjust K to keep it in proportion to feed rate. 

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