TROUBLESHOOTING
6-4
Calibration Errors These error messages can be generated by the open, short, and standard
calibration procedures. If the SR715/720 fails calibration, try running the
procedure again. Repeated failure can indicate a hardware problem. The
parameter limits are fixed and are set so that all units should easily calibrate
within those limits. The messages are listed alphabetically, also listed is the
status value returned by the *CAL? command.
Message Status
Meaning
Cal Error 1 1 Measurement bad due to overload, A/D error, or math error. This error
can occur during short circuit, open circuit, and standard resistor
calibration.
Cal Error 2 2 Impedance measured in short circuit calibration was too large. The
SR715/720 expects the impedance to be <50 Ω, and the resistance to be
less than 10 Ω. Make sure that the fixture has a good low impedance
short in it during short circuit calibration.
Cal Error 3 3 Impedance measured in open circuit calibration. The SR715/720 expects
the impedance to be >10 kΩ at all frequencies and ranges. Make sure
that there are no parts in the fixture during open circuit calibration. Also,
keep hands and other objects away from the fixture during calibration.
Cal Error 4 4 Standard resistor calibration error. The SR715/720 expects that standard
resistor calibration will not change the value of the internal resistors by
more than ±3%. Check to be sure that the correct calibration resistor for
the range being calibrated is in the fixture.
GPIB Problems First, make sure that the GPIB interface is installed. Second, the GPIB address of
the SR715/720 must be set to match that expected by the controlling computer.
The default GPIB address is 17, so it is a good idea to use this address when
writing programs for the SR715/720. Any address from 0 to 30 may be set using
the rear panel switches SW2.
The SR715/720 will ignore its front panel keypad when Remote Enable (REN)
has been asserted by the GPIB. This "REMOTE" state is indicated by the REM
LED. To return to LOCAL operation (i.e. to enable the front panel) press
backspace. Controlling programs may inhibit the ability to return to LOCAL
operation by asserting the Local-Lockout state (LLO).
A linefeed character is sent with End or Identify (EOI) to terminate strings from
the SR715/720. Be certain that your GPIB controller has been configured to
accept this sequence.
RS-232 Problems Make sure that the RS-232 baud rate, parity, and word size are set to match that
expected by the controlling computer. The default settings are 1200 baud, no
parity, 8 bit data. The SR715/720 always sends two stop bits, and will correctly
receive data sent with either one or two stop bits.
When connecting to a PC, use a standard PC serial cable, not a "null-modem"
cable. The SR715/720 is a DCE (Data Communications Equipment) device, and
so should be connected with a "straight" cable to a DTE device (Data Terminal
Equipment). The "minimum" cable will pass pins 2,3 and 7. For hardware
handshaking, pins 5 and 20 (CTS and DTR) should be passed. Occasionally,
pins 6 and 8 (DSR and CD) will be needed: these lines are always asserted by
the SR715/720.
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