Detecting Open Transducers - HP E1419A User Manual

Detecting Open Transducers

NOTES
Chapter 3
Most of the HP E1419A's analog input SCPs provide a method to detect
open transducers. When Open Transducer Detect (OTD) is enabled, the SCP
injects a small current into the HIGH and LOW input of each channel. The
polarity of the current pulls the HIGH inputs toward +17 volts and the LOW
inputs towards -17 volts. If a transducer is open, measuring that channel will
return an over-voltage reading. OTD is available on a per SCP basis. All
eight channels of an SCP are enabled or disabled together. See Figure 3-13
for a simplified schematic diagram of the OTD circuit.
Figure 3-13 Simplified Open Transducer Detect Circuit
1) When OTD is enabled, the inputs have up to 0.2µA injected into them. If
this current will adversely affect your measurement, but you still want to check
for open transducers, you can enable OTD, run your algorithms, check analog
input variables for measurement values that indicate an open transducer, then
disable OTD and run your algorithms without it. The HP E1419A's accuracy
specifications apply only when OTD is off.
2) When a channel's SCP filtering is enabled, allow 15 seconds after turning
on OTD for the filters capacitors to charge before checking for open
transducers.
To enable or disable Open Transducer Detection, use the
DIAGnostic:OTDetect <enable>, (@<ch_list>) command.
Programming the HP E1419A 103