visasession

[Stefano58]

please, Can anyone give me a small application for FP-VISA with a USB meter?

thank you

[Laksen]

It all depends on what meter you are using. The different vendors use different commands to setup and retrieve data.

Here's a quick and dirty example for a Keysight 34411A where the dmm is a TVisaSession component from here(https://github.com/Laksen/FP-VISA):
The address has to be configured to match the USB visa address provided by whatever VISA stack you have installed.

Code: Pascal  [Select][+][-]

1. begin
2.   // Setup for autoranging DC measurements
3.   dmm.Command('CONFigure:VOLTage:DC');
4.   dmm.Command('TRIGger:SOURce BUS');
5.   dmm.Command('INITiate');
6.  
7.   // Do a single measurement
8.   dmm.Command('*TRG');
9.   dmm.Query('*OPC?'); // Wait for trigger
10.   memo1.Lines.Add('Read: "'+trim(dmm.Query('FETCh?')));
11. end;
12.  

[Stefano58]

I also need to install a VISA stack, can you help me?
Thank you for your patience.

[Laksen]

At work I use Keysight IO Libraries (http://www.keysight.com/main/software.jspx?cc=DK&lc=dan&ckey=2175637&nid=-33330.977662&id=2175637), but that's Windows only. For Linux/Mac NI VISA might work, but it's apparently not easy to get working; at least not on Linux.

[Stefano58]

I have already installed VISA library.
The Python script, as reported below, runs with no problem.
--------------------------------------------------------------
>>> import visa
>>> rm = visa.ResourceManager() # create a ResourceManager object
>>> print(rm.list_resources())  # list the available resources
('USB0::0x0699::0x0368::C012494::INSTR', 'ASRL10::INSTR', 'ASRL33::INSTR', 'USB::0x0699::0x0368::C012494::INSTR')
>>> my_inst = rm.open_resource('USB0::0x0699::0x0368::C012494::INSTR')
>>> print(my_inst.query("*IDN?"))
TEKTRONIX,TBS 1102B,C012494,CF:91.1CT FV:v4.0
----------------------------------------------------------------
I installed also the FP-VISA package for Lazarus.
Can anyone translate the Python script into Lazarus?

Thank you

[Laksen]

Try this:

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. uses
4.   session;
5.  
6. var
7.   my_inst: TVisaSession;
8. begin
9.   my_inst:=TVisaSession.Create(nil);
10.   my_inst.Address:='USB0::0x0699::0x0368::C012494::INSTR';
11.  
12.   my_inst.Active:=true;
13.   writeln(my_inst.Query('*IDN?'#10));
14.  
15.   my_inst.Free;
16. end.
17.  

[CM630]

Any idea how to get the list of the available VISA devices?
I tried to use viFindRsrc, but I did not succeed.

[Laksen]

Code: Pascal  [Select][+][-]

1. //Searches for all connected devices, that matches 'filter'.
2. {
3. Filter examples:
4.  ?* -All devices
5.  ?*INSTR -All INSTR capable devices
6.  USB?* -All USB connected devices
7. https://www.ni.com/docs/en-US/bundle/ni-visa/page/ni-visa/vifindrsrc.html
8. }
9. function SearchDevices(const filter: string; devlist: TStringList): longint;
10. var
11.     handle: ViSession;
12.     res: ViStatus;
13.     list: ViFindList;
14.     cnt, i: ViUInt32;
15.     dsc: array[0..255] of ViChar;
16. begin
17.    res := viOpenDefaultRM(@handle);
18.    try
19.       if (res < VI_SUCCESS) then begin
20.          exit(res);
21.       end;
22.  
23.       res := viFindRsrc(handle, pchar(filter), @list, @cnt, dsc);
24.       if (res < VI_SUCCESS) then begin
25.          exit(res);
26.       end;
27.  
28.       if (cnt > 0) then begin
29.          devlist.Clear;
30.          devlist.Add(dsc);
31.          for i:=1 to cnt - 1 do begin
32.             res := viFindNext(list, dsc);
33.             if (res < VI_SUCCESS) then begin
34.                exit(res);
35.             end;
36.             devlist.Add(dsc);
37.          end;
38.       end;
39.       result := res;
40.    finally
41.       viClose(handle);
42.    end;
43. end;
44.  

It should work like that (it works on Keysight IOLibs), but discovery depends on the stack (VXI-11 is discovered with UDP broadcast, HiSLIP is discovered through LXI(mDNS/UDP), USBTMC needs to match driver, ASRL needs to be preconfigured) or whether you have stored any preconfigured devices in the VISA resource manager manually. Basically for network connected devices you need them to be on the same subnet as the host machine

[CM630]

Thanks, in Windows it seems to work fine with NI VISA - I tried it with a Tektronix and a Rigol.
I expanded your example, maybe it could do without a session, I but that is what I had as an example from the forum.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.   visa, visatype, session;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     Memo1: TMemo;
18.     procedure Button1Click(Sender: TObject);
19.   private
20.  
21.   public
22.  
23.   end;
24.  
25. var
26.   Form1: TForm1;
27.  
28. implementation
29.  
30. {$R *.lfm}
31. //Searches for all connected devices, that matches 'filter'.
32. {
33. Filter examples:
34.  ?* -All devices
35.  ?*INSTR -All INSTR capable devices
36.  USB?* -All USB connected devices
37. https://www.ni.com/docs/en-US/bundle/ni-visa/page/ni-visa/vifindrsrc.html
38. }
39. function SearchDevices(const filter: string; devlist: TStringList): longint;
40. var
41.     handle: ViSession;
42.     res: ViStatus;
43.     list: ViFindList;
44.     cnt, i: ViUInt32;
45.     dsc: array[0..255] of ViChar;
46. begin
47.    res := viOpenDefaultRM(@handle);
48.    try
49.       if (res < VI_SUCCESS) then begin
50.          exit(res);
51.       end;
52.  
53.       res := viFindRsrc(handle, pchar(filter), @list, @cnt, dsc);
54.       if (res < VI_SUCCESS) then begin
55.          exit(res);
56.       end;
57.  
58.       if (cnt > 0) then begin
59.          devlist.Clear;
60.          devlist.Add(dsc);
61.          for i:=1 to cnt - 1 do begin
62.             res := viFindNext(list, dsc);
63.             if (res < VI_SUCCESS) then begin
64.                exit(res);
65.             end;
66.             devlist.Add(dsc);
67.          end;
68.       end;
69.       result := res;
70.    finally
71.       viClose(handle);
72.    end;
73. end;
74.  
75. { TForm1 }
76.  
77. procedure TForm1.Button1Click(Sender: TObject);
78. var
79.   mystl: TStringList;
80.   i: integer = 0;
81.   VisaSession1 : TVisaSession;
82.   DeviceInfo: string = '';
83. begin
84.    memo1.Clear;
85.    Application.ProcessMessages; //Needed by Memo1.Clear
86.    mystl := TStringList.Create;
87.    SearchDevices('?*',mystl);
88.    if (mystl.Count < 1) then exit; ;
89.    for i:=0 to (mystl.Count - 1) do
90.    begin
91.      DeviceInfo := mystl.Strings[i];
92.      VisaSession1 := TVisaSession.Create(nil);
93.      VisaSession1.Address := mystl.Strings[i];
94.      //Usaually COM ports do not respond
95.      try
96.        VisaSession1.Active := True;
97.        DeviceInfo := DeviceInfo + ' ➤ ' + VisaSession1.Query('*IDN?');
98.      except
99.        if DeviceInfo.StartsWith('ASRL')
100.        then DeviceInfo := DeviceInfo + ' ➤ Unknown COM port'
101.        else DeviceInfo := DeviceInfo + ' ➤ Unknown';
102.      end;
103.      Memo1.Append (DeviceInfo);
104.      VisaSession1.Active := False;
105.    end;
106. end;
107.  
108. end.
109.  
110.  

But what startled me is that the dynamic-link library is linked ... statically 
Do you have an implementation for dynamic linking? If not, I shall (try to) make.

[Laksen]

Do you have an implementation for dynamic linking? If not, I shall (try to) make.

No, but I was thinking about making one and overhauling it a bit since I've needed to use it on Linux a couple of times where the library discovery process is quite odd

[MarkMLl]

No, but I was thinking about making one and overhauling it a bit since I've needed to use it on Linux a couple of times where the library discovery process is quite odd

I've just been struggling with that one myself, in relation to extending a battery tester program to handle different types of physical device using a shim generator originally written to aid access to system libraries such as libusb.

When considering a backend (etc.) library written in Pascal, placement of a .so for at-startup loading is picky: it's actually easier to use on-demand loading since that allows you to specify the directory explicitly, i.e. "same as executable", "in a backend directory", or whatever.

MarkMLl

[CM630]

An update is attached.
It contains:
1. visa_dyn.pas - dynamic bindings for Visa.
2. An example app for listing the attached Visa devices
3. A list of the visa routines, I used a notepad and a sheets app to create the dynamic bindings.

In the attachment I have replaced visa with visa_dyn in session.pas.
I have not thought on how to make it switchable, maybe it is possible.

The example may work, but it may not work. I have found multiple *visa32*.dll files on one of the PCs.
I have tried 6 or 7 of them.
Most load and the app gets the data, with some DLLs the COM ports are not detected (only the Visa ones), one DLL did not load, one loaded, but crashed on unloading, one loaded, but the app retrieved no data.
I tried Tektronix, Rigol and R&S. The last one did not respond to VisaSession1.Query('*IDN?'), the others did.

Edit: I forgot to take care for 64 bit Lazarus. I guess *visa64.dll shall be used, I will try it next days.

Edit2: I updated the visa_dyn and the example. The example app works when built with Lazarus64 even with visa32.dll but differently: generates exceptions with some COM devices; a single VISA device is found 3 times (twice with the same address, once with USB instead of USB0). Again, I found a *visa64.dll which seems to work normally.

[Laksen]

Looks like a good start. I think it makes sense to only use dynamic linking. The old approach was taken due to laziness

[CM630]

Conversion from static to dynamic is fast and easy, once you do it.
Maybe this function deserves mentioning:

Code: Pascal  [Select][+][-]

1. function GetManufacturer (Address: string): String;
2. var
3.   ManufID : string = '';
4. begin
5.   if (Address = '') then exit ('');
6.   if (Length(Address.Split(['::']))<2) then exit ('');
7.   ManufID:= uppercase(Address.Split(['::'])[1]);
8.  
9.   case ManufID of
10.     '0X0699': Result := 'Tektronix';
11.     '0X1AB1': Result := 'Rigol';
12.     '0X0AAD': Result := 'Rohde & Schwarz';
13.     else Result := ManufID;
14.   end;
15. end;

It seems odd, but I cannot find a list of manufacturer IDs  , maybe you can extend the list with devices that you have available.
And maybe these constants might be added in visatype.pas or somewhere else.
And maybe lowercase is better than uppercase, Visa seems to return a lowercase “x”.

[Laksen]

Those are just USB vendor IDs: https://the-sz.com/products/usbid/index.php?v=0X0699&p=&n=
But I wouldn't trust that, but instead rely on the *IDN? result