Time constant and response time are often different. A time constant is usually the time it takes for a device to go from one state to some percentage (often 63%) of a new state, whereas response time is the time required to achieve a stable state within some tolerance band (+/- 5% for instance). You probably want to state the time it takes for the sensor to stabilize it's reading when exposed to a new solution concentration. Lets say you start with a 10uM glucose solution and switch to a 100uM solution. How fast does the reading from the sensor reach a stable point at the new concentration. If the measurement is stable in one second, you'll have a response time of 90uM/S. If it takes 10 seconds, your response time is 9uM/S. This may vary with concentration so the response time is often stated in a concentration rage where the sensor is most linear. It may also be graphed against the sensitivity of the sensor (response time vs. percent of maximum reading). Hope that helps.

Time constant usually characterises the response of a sensor from sudden change of its initial output signal to the new stable output when sudden changes occur in the system.Physically, the constant represents the time it takes the system's step response to reach 1-1/e or approx 63.2% of its final (asymptotic) value for systems that increase in value (say from a step increase), or it can represent the time for systems to decrease in value to 1/e or approx 36.8% (say from a step decrease). Hence in order to characterise the sensor the response time is usually defined as time required to attain a change from its initial output to 63% of stable output value when a change occurs in the system. The time constant of electrical circuits such as RC or RL circuits is also determined according to the above concept. I hope the reviewer may be interested to know the relation of time constant to band width.

It is often a reasonable assumption to consider that the output signal of the chemical sensor, and thus the chemical concentration that corresponds to this signal level, is affected by a first-order delay (also called lag). The error that results from identifying this measured chemical concentration (Cmeas) with the corresponding actual (real) concentration (Creal), can then be estimated after the following ordinary differential equation, expected to represent the dynamic response of the sensor: τ·dCmeas/dt + Cmeas = Creal, where τ stands for the 'time constant' of the sensor. A step-change imposed to the actual concentration may, in principle, allow for the estimation of the 'time constant'.

References (e.g.):

E. B. Nauman, "Introductory Systems Analysis for Process Engineers", Butterworth-Heinemann Series in Chemical Engineering, Reed Publishing Inc., USA, 1990; R. J. Ord-Smith, J. Stephens, "Computer Simulation of Continuous Systems", Cambridge University Press, 1975.

Note ― The above equation may be helpful for the simulation of chemical systems (e.g. eq. 2.58; next ref.).

Thesis Controlo do Oxigénio Dissolvido em Fermentadores para Minimi...

Dear Ezzaldein.

In amperometric biosensors, the velocity of all process such as: electronic transference, electrónics response of the apparatus, among others, are very quick, and the time of response of the biosensor depends only from the enzymatic kinetic. Diffusion of the substrate toward the enzyme and the product of the enzymatic reaction, toward electrode. When this system is in equilibrium, we say that is in stationary state, and the current of the stationary state (Iss) is proportional at the concentratión of substrate. Consequently, this is the process most slow, and from it depend the time of response of the biosensor. The constant of time, will be, the constant of velocity, or the interchange enzymatic constant. V= Ki Cproduct; I e. I= K Cproduct. K is the constant of time of the biosensor. The design of the biosensor is very important because the technic of inmobilizatión of the enzyme can modify their afinity by the substrate. In this case, the value of Km increase, and consequently the constant of time of the biosensor is high and the time of response of the biosensor increase.

Regards