  The Simons Observatory (SO) is a ground based Cosmic Microwave Background
experiment that will be deployed to the Atacama Desert in Chile. SO will field
over 60,000 transition edge sensor (TES) bolometers that will observe in six
spectral bands between 27 GHz and 280 GHz with the goal of revealing new
information about the origin and evolution of the universe. SO detectors are
grouped based on their observing frequency and packaged into Universal Focal
Plane Modules, each containing up to 1720 detectors which are read out using
microwave SQUID multiplexing and the SLAC Microresonator Radio Frequency
Electronics (\smurf). By measuring the complex impedance of a TES we are able
to access many thermoelectric properties of the detector that are difficult to
determine using other calibration methods, however it has been difficult
historically to measure complex impedance for many detectors at once due to
high sample rate requirements. Here we present a method which uses \smurf\ to
measure the complex impedance of hundreds of detectors simultaneously on
hour-long timescales. We compare the measured effective thermal time constants
to those estimated independently with bias steps. This new method opens up the
possibility for using this characterization tool both in labs and at the site
to better understand the full population of SO detectors.
