SRS Labs Lock-In Amplifier, SR530 RS232 Echo and No Echo Operation, Try-Outwith an ASCII Terminal

The REM LED is on whenever the SR530 is programmed to be in the remote state.

RS232 Echo and No Echo

Operation

In order to allow the SR530 to be operated from a terminal, an echo feature has been included which causes the unit to echo back commands received over the RS232 port. This feature is enabled by setting switch 6 on SW2 to the DOWN position. In this mode, the SR530 will send line-feeds in addition to carriage returns with each value returned and will also send the prompts 'OK>' and '?>' to indicate that the previous command line was either processed or contained an error. Operating the SR530 from a terminal is an ideal way to learn the commands and responses before attempting to program a computer to control the SR530. When the unit is controlled by a computer, the echo feature should be turned off to prevent the sending of spurious characters which the computer is not expecting.

Try-Out with an ASCII Terminal

Before attempting any detailed programming with the SR530, it is best to try out the commands using a terminal. Connect a terminal with an RS232 port to the RS232 connector on the rear panel of the SR530. A 'straight' RS232 cable is required since the SR530 is a DCE and the terminal is a DTE. Set the baud rate, parity, and stop bits to match the terminal by setting SW2 per the switch setting table given on page 7. The echo mode should be enabled (switch 6 DOWN). After setting SW2 and connecting the terminal, hold down the LOCAL key while turning the unit on. This causes the SR530 to assume its default settings so that the following discussion will agree with the actual responses of the SR530. The ACT and ERR LED's on the front panel will flash for a second and the sign-on message will appear on the terminal. Following the message, the prompt 'OK>' will be displayed. This indicates that the SR530 is ready to accept commands.

Type the letter 'P' followed by a carriage return (P<cr>). The SR530 responds by sending to the terminal the characters 0.00 indicating that the phase is set to 0 degrees. In general, a command with no arguments or parameters reads a setting of the unit. To set the phase to 45 degrees, type the command, P45<cr>. To see that the phase did change, use the SELECT key on the front panel to display the phase on the REFERENCE

DIGITAL DISPLAY. Typing the phase read command, P<cr>, will now return the string 45.00 to the terminal.

Now read the gain using the sensitivity read command, G<cr>. The response should be 24 meaning that the sensitivity is at the 24th setting or 500 mV. Change the sensitivity by typing G19<cr>. The sensitivity should now be 10 mV. Check the front panel to make sure this is so.

The Channel 1 Output of the lock-in is read by typing the command, Q1<cr>. The response is a signed floating point number with up to 5 significant digits plus a signed exponent. Change the gain to 10 uV using the G10 command. The response to the Q1 command will now be similar to the previous one except that the exponent is different.

Attach a DC voltmeter to the X6 output on the rear panel. The range should allow for 10V readings. The voltage at the X6 output can be set using the X6 command. Type X6,5.0<cr> and the X6 output will change to 5.0V. To read this back to the terminal, just type X6<cr>. When setting the X6 voltage, the voltage may be sent as an integer (5), real (5.000), or floating point (0.500E1) number. Now connect the X6 output to the X1 input (also on the rear panel). X1 through X4 are analog input ports. To read the voltage on X1, simply type X1<cr>. The response 5.000 should appear on the terminal. The analog ports X1 through X6 can be used by your computer to read outputs of other instruments as well as to control other laboratory parameters.

At this point, the user should experiment with a few of the commands. A detailed command list follows.

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