Rockwell Automation 1395 Digital DC Drive FRN 5-10.10/9.30 - Manual (Page 109)

Chapter 5
Functional Description
5-23
Setting the Trend Buffer Type – Each trend buffer can be set up as a
“one-shot” or “continuous trigger” buffer. When a buffer is set up as a
“one-shot” it is turned off after all post samples have been taken. At this
time, the trend enable parameter value is changed to OFF effectively
disabling that trend buffer. The buffer will retain the data from the most
recent trigger until it is manually activated or turned ON.
A “continuous trigger” trend buffer operates continuously, even if it is
triggered multiple times. When a new trigger condition occurs, the
previous data samples are overwritten.
Activating a Trend Buffer – Each trend buffer can be independently
turned on or off. A deactivated trend buffer will not monitor the selected
parameter or evaluate trigger conditions.
If a trend buffer is set to “one shot”, the Drive will set the Trend Enable
parameter to “OFF” when it has been triggered.
Setting the Trend Buffer Output Rate – Each trend actually consists of
two separate buffers. One buffer is used during the monitoring and post
sampling periods to store data samples. The second is used once a trend
has finished sampling.
When a trigger condition occurs and all post samples have been taken, the
data is transferred to an output buffer. At this time, it is available for
display by a programming terminal or for an output to an external device.
When directed to an external device, the data sample output rate can be
adjusted. The range is 4ms to 30 seconds per data sample (in 4ms
increments). A programmable output rate allows you to connect a wide
variety of devices (chart recorders or oscilliscopes for example) to an
analog channel or an adapter board and view the sampled data, regardless
of the speed of the device.
A positive spike followed immediately by a negative spike is also output,
to indicate the start of the data samples. Data is continuously transmitted
until the trend is restarted or if the Trend output configuration link is
removed.
ATTENTION: Doing an EE recall or initialize function will
cause termination of any executing trends, and of those trends
contained in EEPROM. An EEPROM store function has no
effect on Trend execution.
The trend buffers can be programmed to provide an expanded number of
data samples beyond the standard 100 samples. This is accomplished by
programming a second trend to trigger when the ENABLE parameter in the
first trend is turned off. The maximum number of samples that can be
taken is 400.