- A composition sensor is used to continually monitor the contaminant level in a liquid stream. The dynamic behavior of the sensor can be described by a first-order transfer function with a time constant of 10 seconds, C'm(s) 1 C's) 10s + 1 where C' is the actual contaminant concentration and cm is the measured value. Both are expressed as deviation variables (e.g. C'=C-C). The nominal concentration is = 5 ppm. Both C and c'm have values of 5 ppm initially (at t = 0). = An alarm sounds if the measured value exceeds the environmental limit of 7 ppm. Suppose that the contaminant concentration C gradually increases according to the expression C(t) = 5 + 0.2t, where t is expressed in seconds. After the actual contaminant concentration exceeds the environmental limit, what is the time interval, At, until the alarm sounds? Sketch the Cm-t graph. =