To control a 3rd party calibrator via RS232 or GPIB requires understanding of the remote operation and commands structure of the instrument, this is often described in the instruments user manual.
When creating or editing tests in an EasyCal a procedure, a GPIB or RS232 control command can be entered manually. An example command might be ‘OUT 5V,20 kHz’ which sets a Fluke 5500A output to 5V 20kHz AC, and then by adding the ‘OPER’ command, the output is switched on.
EasyCal includes a command syntax which can be used to simplify the task of creating the commands and allow EasyCal pre-written library procedures to be quickly adapted for use with 3rd party calibrators. In this application note the Value, Units and Valbase substitution syntax is used so that the same command can be applied to multiple tests, speeding up procedure development.
Usage: Value and Units substitution
When EasyCal processes a GPIB or RS232 command to send to a third party instrument, it recognises special syntax which gets substituted for values that are relevant to the test being performed. The following screenshot and table illustrates the automatic substitution:
By using {VAL} and {UNITS} the required value and its units specified in the test are transmitted to the calibrator. Using this method a single command can be used for multiple tests.
The following substitution commands are available, with example output of a test setup for a required value of 90mV:
Command Syntax
Substitution Description
Example Output
{VAL}
Required value as specified in the test editing menu
90
{UNIT}
Units of the required value
mV
{VALBASE}
Required value converted into the base unit
0.09
Note: For resistance functions EasyCal always transmits {UNITS} as ‘OHMS’.
It is now possible to use the same command for multiple tests, since EasyCal will substitute in the required value. To edit multiple tests simply highlight the required tests and click edit:
The command entered in the ‘Edit Multiple Test’ screen is then applied to all tests selected.
Application: Controlling a Fluke 5500A
The following commands are used to control a Fluke 5500A using RS232. Since the control is via RS232 the terminating character needs to be added to the end of the command, for a Fluke 5500A this is {10}.
All non AC functions OUT {VAL}{UNITS};OPER{10}
AC functions (requires the frequency to be set within the command) OUT {VAL}{UNITS},60Hz;OPER{10}
To set the Fluke into ‘STAND BY’ STBY{10}
Application: Controlling a Wavetek 9100
The following commands are used to control a Wavetek 9100 using GPIB.
DC Volts Before Test :OUTP OFF;:FUNC DC;:VOLT {VALBASE};:OUTP ON After Test :OUTP OFF
DC Current Before Test :OUTP OFF;:FUNC DC;:CURR {VALBASE};:OUTP ON After Test :OUTP OFF
AC Volts, requires the frequency to be set within the command (this command is at 50Hz). Before Test :OUTP OFF;:FUNC SIN;:FREQ 50;:VOLT {VALBASE};:OUTP ON After Test :OUTP OFF
AC Current, requires the frequency to be set within the command (this command is at 50Hz). Before Test :OUTP OFF;:FUNC SIN;:FREQ 50;:CURR {VALBASE};:OUTP ON After Test :OUTP OFF
Example; use advanced setting to enter before and after test commands:
Measuring using GPIB/RS232 commands
During the calibration run the device under test’s reading is entered in the normal manor via keyboard or up/down controls.
Readback from a DMM or other measuring device
Some instruments such as certain DMMs and oscilloscopes can automatically transmit their readings to a computer via GPIB or RS232 communications. EasyCal can take these readings by using the “readback” feature.
By using readback, EasyCal procedures can be developed to automatically get readings from the calibrating equipment or device under test without any operator input. This allows fast and efficient calibration as well as minimising operational errors.
The instrument providing the readback must:
Be equipped with an RS232 serial port or a GPIB port.
Have a suitable cable for connection to a PC. In the case of GPIB instruments, this will be normally be a standard GPIB cable. In the case of an RS232 serial cable it will often be either supplied with the instrument or as an option.
In addition, you need to know:
The format of the readback data that is returned by the instrument, e.g. “<VALUE>,<ERROR_CODE>,<CR>”
What RS232/GPIB command must be sent to the instrument to perform a single readback, e.g. “:MEAS?” is often used for SCPI-compatible instruments
This information is specific to each type of instrument. It should be found in the user manual of the instrument.
EasyCal supports the following GPIB Cards:
National Instruments: PCI/USB
Adlink: PCI / USB
Agilent: PCI/USB
Example commands for measuring instruments:
HP34401A / Fluke 884x
Reset the unit to the default state syst:rem;:*rst{10}
Make a measurement in the default function (DCV) syst:rem;:meas?{10}
Make a measurement in the DC Current function (DCV) syst:rem;:meas:CURR:DC?{10}
Note the command separators between syst:rem and the following commands. A ;: is used to return to the top level.
syst:rem;:meas:CURR:DC?{10}
This is the same as the following commands syst:rem{10} meas:CURR:DC?{10}
