The Model 680 is a user selectable voltage or current simulator. It is useful for the setup and testing of process controllers and indicators with either a current loop or control voltage input, such as liquid level controllers and other devices. The mode of operation is displayed on the top line of the LCD. Either 4-20mA, 0-20mA, 0-10V, or 0-5V. The Model 680 can be set to any one of these four modes of operation by holding down the rotary push-button until the desired mode is displayed. The mode is saved in nonvolatile memory so that the device will power up in the mode last selected. The output signal level is displayed on the bottom line of the LCD. On power up or on changing the mode of operation, the output goes to the range minimum, i. e. 4mA, 0mA, or 0V. The Model 680 offers short circuit protection by actively sensing for any overload condition and limiting output current to 20mA. Overload at the output is indicated by OL on the top line of the LCD and occurs when the output current is 21mA or greater. Signal level is adjustable with the rotary dial in increments of 0.1mA or 0.1V, or you can depress the dial to quickly jump between the minimum and maximum values of the range.