Draw a schematic of a gas-fired furnace. The furnace has a temperature measurement of the outlet temperature of the process fluid, a flow measurement on the process fluid, a flow measurement for the fuel to the furnace and control valve on the fuel line to the furnace. The objectives are:

a. A control system that adjusts the ratio of fuel flow to the flow rate of the process fluid to control the outlet temperature of the process fluid

b. A flow control loop is used to maintain the measured fuel flow rate of the level specified by the ratio controller