Fluke PM6685R, PM6681R manual Display Control, Time Measurement Resolution, Gpib Data Format

How to Measure Fast

AUTO

One of the most timesaving commands you can use with the CNT-8X is :INPut:LEVel:AUTO￿OFF. This will save the time it takes to determine the trigger levels. (About 50ms/measurement in PM6680B and PM6685, and 85ms in PM6681.)

Display Control

The display can be switched off with the command DISPlay:ENABle￿OFF. When you switch off the display, the counter loses the measurement data resolution informa- tion. This means that the counter always sends all digits independently of whether or not they are significant. This command reduces the dead time by about 7ms.

Time Measurement

Resolution

The basic time measurement resolution can be selected by using the command SENSe:ACQ:RES￿«HIGHLOW».

When you set the resolution to low it will be 100ns for PM6680B and PM6685, and 80ns for PM6681. Instead of the high res- olution, which is 0.25ns for PM6680B and PM6685, and 0.05ns for PM6681.

If the counter does real-time calculations and you switch to low resolution, the measurement dead time decreases about

0.6to 0.9ms. If the counter does not do real-time calculations, then it saves only about 0.05ms per measurement cycle. If the counter does real time calculations with the display switched on, then you can save up to 2ms by selecting the lower resolution.

GPIB Data Format

You can select the format of the result sent on the GPIB using the FORMat

command. Two options exist: ASCii and REAL. The REAL format saves a lot of time both in the instrument and the con- troller for converting data. However, when the counter uses the REAL format, you lose the measurement data resolution information. It sends the REAL format as a block data element. This means that it sends data as:

#18< 8 bytes real>.

The <8 bytes real> is a double precision binary floating-point code according to IEEE 488.2 / IEEE 754.

Automatic Interpolator Calibration (PM6680B/85)

The time interpolation technique achieves the high time resolution. The counter au- tomatically calibrates these interpolators once per measurement cycle. You can control this automatic calibration by us- ing the command:

CAL:INT:AUTO￿ «ONOFFONCE».

When you switch calibration off, the measurement cycle time decreases.

Disabling this calibration makes the counter more sensitive to temperature changes. The measurement values may drift away, which results in a larger inac- curacy. However, when the instrument has been switched on for more than 20 minutes and the ambient temperature is stable within ± 5°C, this is no problem. You can also easily recalibrate the

7-8 General Speed Improvements