Pole/Ratio Mode (0); Reading Interval And Delay Programming - Keithley 199 Instruction Manual

NOTES:
1. in order to use all eight channels in the 2-p& mode,
the A and B outputs must be connected in parallel with
the DMM inputs, as discussed in paragraph 2.11.
2. When using the scanner with data store, the number
of sets of data that are stored is determined both by the
data store size(I) command, as well as the number of
channels per scan. For example, with a programmed size
of 400 readings, and a scan limit of eight channels, 50
sets of data will be stored (4CHYS=SO).
3. A "CHAN 4 MAX" error will occur if you attempt to
program a limit greater than 4 with the unit in the 4-p&
mode.
4. Sending a scanner command with no scanner installed
will result in an "IDDC" error.
Programming Example-To demons&ate scanner program-
ming, close channel 3 by entering the following statenwnts.~
Note that the dosed channel (3) is displayed in the right-
most digit.
To open the channel and return the display to normal,
enter the following statement.
3.12.2 Pole/Ratio Mode (0)
The O~command controls 214 pole normal mode opera-
tion, as well as 2/4 pole ratiooperation. In the 2-pole mode,
up to eight channels can be scanned, while a maximum
of four channels can be scanned in the 4-pole mode.
NOTE
Jf you attempt to program the 4-pole mode with
channels 5-8 already closed, the pole mode will
not be changed and a "CHAN 4 MAX" error will
occm The closed channel will not be opened.
In the ratio mode, the unit computes the ratio between
the channel 2 through 8 reading to the channel 1 reading.
in order to determine ratio, the unit first takes a reading
on channel 1, and then computes the ratio for the remain-
ing channels as follows:
CHl
Where: R = ratio
CHn = channel number (2 through 8)
CHl = channel 1
The result is then s&t over the bus as requested or stored
in the data store buffer if enabled. Ratio values are iden-
tified with the RAT prefix in the data string, which is
discussed more fully in paragraph 3.9.12.
Upon power up, or after a DCL or SDC, the 00 (2-pole)
mode will be in effect.
Programming Example--Enter the statements below to
program the unit to operate in the 4-p& mode.
3.12.3 Reading interval and Delay
Programming
The progratimed reading interval determines the time
period between channels in the step mode, and the time
period between setsof channels in the scan mode. Inter-
val is programmed with the Q command as follows:
Qo = Default interval, l75msec (SELECT ON)
Qn = User programmed interval
Here, n is the interval time in milliseconds, with an
allowable range of I.5 to 999 PPPmsec. The factory default
value for interval is l75msec. The ifistrument will assume
that value upon power up, or after a DCL or SDC.
A channel settling time can be programmed by using the
delay (W) command. When a scan delay is used, the in-
strument will wait the programmed delay period after clos-
ing a channel before taking a reading. Thus, the delay
period acts as achannel settling time to allow signals to
settle before each measurement.
The scan delay (settling time) can be programmed be sen-
ding the W command as follows:
Wn
3-39