Application note 208

Using the External Instruments function on the GRS500







The GRS500 External Instrument function allows the GRS500 user to link the GRS500 to external test/measurement equipment. The operator typically would use the facility to make test or troubleshooting measurements in addition to the signatures provided by the GRS500; for example measurements could include resistance or voltage tests or a low frequency signal displayed on an oscilloscope.

Note: The Switchable Commons card (part number MSA256) will be required for external instrument operation. Ensure the card is fitted prior to selecting External Instrument operation 

Ensure that the GRS500 hardware and measurement system will support the extra channels required for external control. Select the GRS500 rear panel socket configuration from the Config|External Instruments screen (shown below refer to the socket layout on the rear panel).

Note: Only the 4 socket choices allow the use of the External Instruments option. By default the 3 socket option is selected, (disabling the External Instruments option).

Specifying the External Instrument operation option enables the External Instrument button on the main toolbar. Clicking the External Instrument button switches control from the GRS500 software to an external program.

Connection for external instrument

Connection for external instrument is by two 4mm sockets.
Maximum voltage is 40VDC
Frequencies above 1MHz are not recommended as the probe has no provision for a ground connection.
There is no possibility of using an oscilloscope probe or any device other than the standard GRS probe .

Auxiliary power to the device under test.

A 25 way cable runs from the table to the back panel.  This may be used to take signals or power to the device under test.  No switching is provided so the user must arrange to remove all power and signals when making ASA measurements. Current rating is 300mA per pin, 40V max.

GRS500 External Instruments Programming Interface

Note: The information given here assumes the programmer is familiar with Visual Studio v6 and the use of objects.

The GRS500 External Instruments Programming Interface allows the GRS500 user to write a small program to allow the prober to go to any pin/testpoint in the currently running GRS500 program.  The Programming Interface also provides control of the switchable COM set-up.  This user created program would normally run after the GRS500 tests had run. Programming information is shown below.


The GRS500 object has one class called ExternalInstruments

The Class has six members


Display Prober Alignment dialog


Homes Prober


Requests prober to move to specified pin on loaded GRS database

Boolean=GRS500.Prober_MoveToComponentPin(strComponent, strPin)

If Boolean equals False then strComponent, strPin were not found


Probe down at current location


Probe up


Requests prober to switch Commons.


Where intSwitchableCommonsValue equals one of the following values :

Prober Common 1 = 8

Prober Common 2 = 4

Prober Common 3 = 2

Prober Common 4 = 1

Prober All Commons = 15

A sample External  Instruments test application (including source code) is available in the GRS500 installation folder

Polar Instruments Ltd

Tel: +44 1481 253081 Fax: +44 1481 252476

Polar Instruments 2003. Polar Instruments pursues a policy of continuous improvement. The specifications in this document may therefore be changed without notice. All trademarks recognised.