The choice of a constant current source as the sensor bridge power supply was based on previous works that show a remarkable reduction in the temperature coefficient of the bridge sensitivity [15�C18].Figure 1.Variables definition in the Wheatstone bridge before compensation.If a current sensor is considered, its non-compensated output, vo,nc could be given by:vo,nc (t)=S(t)?i+vo,off(1)being somehow Inhibitors,Modulators,Libraries i the current to be sensed (measured in amps), vo,off the sensor output at zero input current (in mV), t the temperature (in ��C) and S(t), the sensor sensitivity (in mV/A). The output offset could not be considered if this has been compensated previously by calibration. As equation (1) shows, a change in temperature will produce a change in the sensor sensitivity generating an output sensor variation, but without any change in the current i to be measured.

Let S����SvB,nc be the sensor sensitivity normalized to bridge voltage, vB,nc. If the sensor bridge is driven by a constant current iB,nc the voltage drop across it will be:vB,nc (t)=iB,nc?RB (t)=no?iref?RB (t)(2)where RB is the equivalent bridge resistance. The constant current Inhibitors,Modulators,Libraries iB,nc in equation (2) is supplied by the GIC circuit and it is equal to the product of the constant no times the GIC input reference current iref, [13,14]. As a consequence, the non-compensated sensor bridge output vo,nc will be Inhibitors,Modulators,Libraries given by:vo,nc (t)=S��(t)?vB,nc (t)?i=S��(t)?iB,nc?RB (t)?i=S��(t)?no?iref?RB (t)?t(3)Equation (3) shows that the temperature drift of the sensor output will be provided by both normalized sensitivity and bridge equivalent resistance temperature dependences.

It is assumed that before Inhibitors,Modulators,Libraries compensation iref is a good reference current and it is not affected by the temperature.The main purpose of the compensation method is to place enough temperature dependence in iref to compensate the drift in vo,nc(t) caused by (t) and RB(t). As a result the compensated sensor output, vo,c(t) will have no temperature dependence:dvo,c (t)dt=0.(4)Figure 2 depicts how a practical GIC circuit supplies to the bridge sensor Anacetrapib a current iB proportional to a 100 ��A www.selleckchem.com/products/wortmannin.html reference current iref. The gain factor no depends on GIC resistances R1 to R4, a proper replacement of one of them by a series association of a temperature sensor Rs(t) and a constant resistance R will lead to accomplish equation (4). The final objective of the compensation method will be to find a properly selected R resistance value.Figure 2.Driving the MR current sensor by a constant current source using a GIC circuit.