Reading delta values from R&H spectrum analysers - c++

Question

I am currently working on a project where I need to read the difference between the minimum
and maximum markers of a Rhode and Schwarz FSC3 device. I am using NIVisa to connect to the
device over an ethernet connection and pass SCPI commands to it.
The operating system I am using is Ubuntu 20.04.
The code I am using is as shown below -
// Gloabl Visa ResouceManager reference
VisaResourceManager rm;
/**
* Custom type that defines a relation between the deviceIP string
* and a session_t within the Resource Manager
**/
typedef std::map<std::string, VisaResourceManager::session_t> deviceIpSessionMap_t;
deviceIpSessionMap_t devices;
bool device_exists(const std::string deviceIP)
{
deviceIpSessionMap_t::iterator iter = devices.find(deviceIP);
if (iter != devices.end())
{
return true;
}
else
{
return false;
}
}
// --------------------------------------------------------
// Struct defining the ReadConfiguration which is required
// to get readings from the device
// --------------------------------------------------------
struct ReadConfig
{
// The center frequency for the reading
std::string center;
// The span for the reading
std::string span;
// rbw value for reading
std::string rbw;
// vbw value for reading
std::string vbw;
// IP address of the X-pole device
std::string ip;
};
/**
* This function retrieves values from the
* spectrum analyser
*/
int getValueFromDevice(ReadConfig &conf)
{
try
{
//-----------------------------------------------------------
// Set SCPI commands strings
//-----------------------------------------------------------
std::string DeviceIP = "TCPIP::" + conf.ip;
std::string CenterFreq = "FREQ:CENT " + conf.center + "KHz";
std::string Span = "FREQ:SPAN " + conf.span + "KHz";
std::string Rbw = "BAND " + conf.rbw + "KHz";
std::string Vbw = "BAND:VID " + conf.vbw + "Hz";
// logConf(DeviceIP, CenterFreq, Span, Rbw, Vbw);
// Check if the session already exists and reuse it
// if available. If not create a new session and add it
// to the deviceIP to session map
VisaResourceManager::session_t session;
if (device_exists(conf.ip))
{
session = devices[conf.ip];
}
else
{
session = rm.connect(DeviceIP);
devices[conf.ip] = session;
}
session->write("*RST;*CLS\n"); // Reset and clear the device
//-----------------------------------------------------------
// ID the device:
//-----------------------------------------------------------
// session->write("*IDN?");
// std::cout << "status byte = " << session->readSTB() << std::endl;
// std::cout << "*IDN? = " << session->read() << std::endl;
// std::cout << "status byte = " << session->readSTB() << std::endl;
//-----------------------------------------------------------
// Basic Device Settings:
//-----------------------------------------------------------
session->write(CenterFreq); // Setting the center frequency
session->write(Span); // Setting the span
session->write(Rbw); // Setting the RBW
session->write(Vbw); // Setting the VBW
session->write("CALC:DELT1 OFF"); // Removes/resets MARK2 position
session->write("CALC:DELT2 OFF"); // Removes/resets MARK2 position
session->write("CALC:MARK1 OFF"); // Removes/resets MARK1 position
session->write("CALC:MARK2 OFF"); // Removes/resets MARK1 position
session->write("*OPC?"); // Using *OPC? waits until all the instrument settings are finished
//-----------------------------------------------------------
// Setting marker to min and reading the marker Y
//-----------------------------------------------------------
session->write("CALC:DELT1:MIN");
session->write("CALC:MARK1:MAX");
session->write("*OPC?");
session->write("CALC:DELT1:Y?\n");
std::string min = session->read();
int iMin = abs(std::stoi(min));
// std::cout << "iMin : " << iMin << '\n';
//-----------------------------------------------------------
// Disconnect from Device
//-----------------------------------------------------------
// rm.disconnect(session);
return iMin;
}
catch (VisaException ex)
{
std::cout << ex.what() << " -- " << VisaResourceManager::statusDescription(ex.getErrorCode()) << std::endl;
return 0;
}
catch (...){
std::cout << "Encountered an unknown error" << std::endl;
return 0;
}
}
This usually shows me the correct values, but when the analyzer has been on for a while it starts
malfunctioning/reporting absurd values that are too high.
What am I doing wrong ?