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How to use 34401 to get the voltage reading at 1000time/s sample rate

Question asked by viqfoai on Aug 3, 2017
Latest reply on Aug 10, 2017 by tomc

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I am using 34401 to measure DC voltage, I want to sample the voltage at the rate of 1000 times per second. I am trying to get 450 readings at the speed, but the it takes me 1s+ to get it done, below is the configuration I made for this test

CONF:VOLT:DC

TRIG:SOUR BUS

TRIG:COUN 1

VOLT:NPLC 0.02

SAMP:COUN 450

TRIG:DEL 0.0006

After sending above command sequence, I issue the command INIT followed by *TRG, then I send a FETC? to raise the event to PC, but I found it takes 1.8+s for the program to run into the event handler entry from the time point right before sending the *TRG command.

Can some one help to point out what's wrong with above command sequence?

tomc Aug 10, 2017 9:52 AM

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Unfortunately no. This very old DMM only has a 512 reading memory buffer, and the IO processor is slow by today's standards. You should be able to do 500 readings at a time switching back and forth between the two. The actual measurements will be at the higher rate, but there will be a time gap switching between the two instruments.

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tomc Aug 7, 2017 2:21 PM
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First of all you need to use a fixed range and turn auto zero off (CONF:VOLT:DC 100, ZERO:AUTO OFF). The maximum reading rate also requires turning off the front panel display (DISP OFF), and just sending the readings to internal memory. With these settings timing INIT; *OPC?, I get right around 1000 readings/sec.
With trigger source bus and FETCH? for 500 readings over GPIB, I get about 560 readings/sec. The INIT takes a little time to complete before measurements start. Timing INIT:FETC? to complete, I get 416 readings/sec.
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viqfoai Aug 10, 2017 3:29 AM
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Hi, Tom

Thanks for your reply, I get 1000 reading per second according to your suggestion, but now I have two meters to handle, one meter to read voltage, another read current, but I can not get 1000 reading from each meter within 1s, I can only get all 2000 reading from the 2 DMMs in about 2s. since two instruments are working independently, do you think it is possible to get 1000 reading from each DMM in parallel in 1s?

#include<Windows.h>
#include <visa.h>
#include <stdlib.h>
#define READING_COUNT 1000
int main()
{
ViStatus status;
ViSession defaultRM, gpibSesn1, gpibSesn2;
ViBuf pviBuffer;
ViUInt32 retCount;
ViEventType etype;
ViEvent eventContext;
/* Begin by initializing the system */
pviBuffer = (char *)malloc(16 * READING_COUNT + 1);
status = viOpenDefaultRM(&defaultRM);
if (status < VI_SUCCESS) {
/* Error initializing VISA...exiting */
return -1;
}
/* Open communication with GPIB device at primary address 2 */
status = viOpen(defaultRM, "GPIB0::21::INSTR", VI_NULL, VI_NULL,
&gpibSesn1);
status = viOpen(defaultRM, "GPIB0::23::INSTR", VI_NULL, VI_NULL,
&gpibSesn2);
/* Allocate memory for buffer */
/* In addition, allocate space for the ASCII NULL character */

/* Tell the driver what function to call on an event */
status = viEnableEvent(gpibSesn1, VI_EVENT_IO_COMPLETION, VI_QUEUE, VI_NULL);
status = viWrite(gpibSesn1, "*RST\n", strlen("*RST\n"), &retCount);
status = viWrite(gpibSesn1, "FUNC:VOLT:DC\n", strlen("FUNC:VOLT:DC\n"), &retCount); //enable message available and standard event interrupt in service request register
status = viWrite(gpibSesn1, "DISP OFF\n", strlen("DISP OFF\n"), &retCount);
status = viWrite(gpibSesn1, "VOLT:DC:RANGE:AUTO OFF\n", strlen("VOLT:DC:RANGE:AUTO OFF\n"), &retCount);
status = viWrite(gpibSesn1, "ZERO:AUTO OFF\n", strlen("ZERO:AUTO OFF\n"), &retCount);
status = viWrite(gpibSesn1, "CALC:STAT OFF\n", strlen("CALC:STAT OFF\n"), &retCount);
status = viWrite(gpibSesn1, "TRIG:DEL 0\n", strlen("TRIG:DEL 0\n"), &retCount);
status = viWrite(gpibSesn1, "TRIG:SOUR IMM\n", strlen("TRIG:SOUR IMM\n"), &retCount);
status = viWrite(gpibSesn1, "VOLT:NPLC 0.02\n", strlen("VOLT:NPLC 0.02\n"), &retCount);
status = viWrite(gpibSesn1, "SAMP:COUN 1000\n", strlen("SAMP:COUN 1000\n"), &retCount);
status = viEnableEvent(gpibSesn2, VI_EVENT_IO_COMPLETION, VI_QUEUE, VI_NULL);
status = viWrite(gpibSesn2, "*RST\n", strlen("*RST\n"), &retCount);
status = viWrite(gpibSesn2, "FUNC:VOLT:DC\n", strlen("FUNC:VOLT:DC\n"), &retCount); //enable message available and standard event interrupt in service request register
status = viWrite(gpibSesn2, "DISP OFF\n", strlen("DISP OFF\n"), &retCount);
status = viWrite(gpibSesn2, "VOLT:DC:RANGE:AUTO OFF\n", strlen("VOLT:DC:RANGE:AUTO OFF\n"), &retCount);
status = viWrite(gpibSesn2, "ZERO:AUTO OFF\n", strlen("ZERO:AUTO OFF\n"), &retCount);
status = viWrite(gpibSesn2, "CALC:STAT OFF\n", strlen("CALC:STAT OFF\n"), &retCount);
status = viWrite(gpibSesn2, "TRIG:DEL 0\n", strlen("TRIG:DEL 0\n"), &retCount);
status = viWrite(gpibSesn2, "TRIG:SOUR IMM\n", strlen("TRIG:SOUR IMM\n"), &retCount);
status = viWrite(gpibSesn2, "VOLT:NPLC 0.02\n", strlen("VOLT:NPLC 0.02\n"), &retCount);
status = viWrite(gpibSesn2, "SAMP:COUN 1000\n", strlen("SAMP:COUN 1000\n"), &retCount);
while (1)
{
//status = viWrite(gpibSesn1, "FUNC:VOLT:DC\n", strlen("FUNC:VOLT:DC\n"), &retCount);
status = viWrite(gpibSesn1, "ZERO:AUTO ONCE\n", strlen("ZERO:AUTO ONCE\n"), &retCount);
status = viWrite(gpibSesn1, "READ?\n", strlen("READ?\n"), &retCount);
status = viReadAsync(gpibSesn1, pviBuffer, 16 * READING_COUNT, &retCount);
status = viWrite(gpibSesn2, "ZERO:AUTO ONCE", strlen("ZERO:AUTO ONCE\n"), &retCount);
status = viWrite(gpibSesn2, "READ?\n", strlen("READ?\n"), &retCount);
status = viReadAsync(gpibSesn2, pviBuffer, 16 * READING_COUNT, &retCount);
status = viWaitOnEvent(gpibSesn1, VI_EVENT_IO_COMPLETION, VI_INFINITE, &etype, &eventContext);
status = viWaitOnEvent(gpibSesn2, VI_EVENT_IO_COMPLETION, VI_INFINITE, &etype, &eventContext);
if (status < VI_SUCCESS) {
/* Waveform not received...exiting */
unsigned short usStatus;
status = viReadSTB(gpibSesn2, &usStatus);
free(pviBuffer);
viClose(defaultRM);
return -1;
}
}
//Sleep(300);
return 0;
}
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tomc Aug 10, 2017 9:52 AM
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Unfortunately no. This very old DMM only has a 512 reading memory buffer, and the IO processor is slow by today's standards. You should be able to do 500 readings at a time switching back and forth between the two. The actual measurements will be at the higher rate, but there will be a time gap switching between the two instruments.
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How to use 34401 to get the voltage reading at 1000time/s sample rate

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