The use of biological fluid samples in as-sessing tobacco smoke consumption

An arrangement for compensating for changes in the output of a corotron due to environmental changes. The arrangement includes a control corona device and a controlled corona device, the controlled corona device located in a xerographic reproduction machine in a position to deposit charge on an imaging surface and the control device located remote from said imaging surface and inoperative to deposit charge thereon, but exposed to the same environmental conditions of pressure and temperature, etc. The control corotron is connected in electrical parallel with the controlled corotron, which may be one or all of the corotrons used in the xerographic process, so that changes in the current flow in the control corotron due to the environment effect the voltage applied to the controlled corotron to produce a more stable output therefrom.