LIQUID CHILLER CONTROL; ANALOG SENSOR MEASURES CONCENTRATION OF LITHIUM BROMIDE IN SYSTEM

An over-concentration control system for use with an absorption machine (30) of the type having either a single, double and triple effect cooling and heating cycle, which uses lithium bromide in solution with water as the operating liquid. The operating liquid being characterized by a concentration indicative of the quantity of lithium bromide dissolved in water, and by a phase diagram having a crystallization boundary that defines the combinations of concentration and temperature which correspond to a condition of saturation in the solution. A sensing means (10) is provided at a predetermined location within the system which is responsive to the depth of said solution for generating a concentration signal indicative of the concentration of the liquid. A temperature sensor is also provided for generating a temperature signal indicative of the temperature of the liquid. Further means are provided which are responsive to the temperature signal and the concentration signal for calculating a representation of the absorption cycle of the machine (30) which may be plotted on a phase diagram for the lithium bromide system. The representation includes a plurality of critical state points (9,14) which are defined by predetermined respective combinations of concentration and temperature. Means are also provided for comparing the actual concentration and temperature of the liquid to concentrations and temperatures which lie on the said crystallization boundary for lithium bromide for generating a difference signal. Control means are provided which are responsive to the magnitude of the difference signal for changing the operating state of said machine (30) as necessary to prevent the liquid from reaching a combination of concentration and temperature that lies on the crystallization boundary.