Keithley 706 Instruction Manual page 24

The display in the daisy chain configuration includes an addi-
tional digit to accomodate up to 500 channels, 1000 channels
in l-pole mode. The display is shown as follows:
I ml If 01
L I
NOTE
Scanning at a high rate of speed in the daisy
chain configuration may not show the scanned
channels on the mainframe's display.
Example 5 Temperature Scan-With the Model 7057A
thermocouple scanner card, the Model 706 can scan
temperature points. Since the Model 7057A combines the
functions of a thermocouple scanner and uniform
temperature reference it is especially useful for scanning
thermocouples. The input terminals are #lO alloy copper set
in an isothermal block to minimize temperature differences. A
thermistor sensor within the isothermal block is used with a
bridge network located on the Model 7057A. The
temperature of the heat sink is used to calculate the corrected
thermocouple output. The output voltages of each thermo-
couple must be converted to temperature (OC or OFI using ap-
propriate thermocouple tables or polynominal equations.
These equations and tables are provided in the Model 7057A
Instruction Manual.
In this example the Model 706 will be programmed to scan 25
separate temperatures. The following parameters will be pro-
grammed into the Model 706.
1. First channel is 1.
2. Last channel is 25.
3. Number of poles is 2.
4. Interval time is 3 seconds.
5. Use the continous scan mode.
Step
1
2
3
4
9
10
NOTE
Channels 1, 11 and 21 are the temperature
references for the cards.
Use the steps outlined in Table 2-11 to program the Model
706 for the preceding parameters.
As you can see this temperature scan example is quite similar
to the continuous scan example (example 3). The only ap-
preciable difference is the type of scanner card used in each
example. Except for specified values of the parameters
selected, front panel operation is similar in all scanning se-
quences. _
For more detailed information concerning temperature scans
refer to the Model 7057A Instruction Manual.
Example 6 Low Current Scan-With the Model 7058 in-
stalled, the Model 706 is capable of scanning currents in the
range of picoamps. The Model 7058 is a low current scanner
card that is field installable in the scanner mainframe. The
Model 7058 is designed to introduce a minimum of offset cur-
rent (c IpA), while guarding ensures that high isolation
(10153) is maintained between input signals.
The actual measurement of the low current should be done
with a high quality electrometer such as the Model 614 or
Model 619. A high quality picoammeter such as the Keithley
Model 480 could also be used. All three of these instruments
are capable of measuring in the range of picoamps with high
accuracy. To measure such low currents a number of
measurement parameters such as, input impedance, cabling,
measuie~ment~ configuration, a&.,- must be taken into con;
sideration. This example does not attempt to give instructions
on low current measurement, the instruction manuals pro-
vided with each of the previously mentioned electrometers
Table 2-11. Temperature Scan Example
Action
Install a Model 7057A into
slots 1, 2 and 3 of the
Model 706.
Select appropriate line voltage
and turn on the Model 706.
Press PRGM, 6.
Press 2, ENTER.
Press 0, 0, 1, FIRST.
Press 0, 2, 5, LAST.
Press INTERVAL, 0, 0, 3, 0,
0, 0, 0, ENTER.
Press CHANNEL, RESET.
Press CONTINUOUS.
Press START/STOP.
Comments
Refer to paragraph 2.2.2.
Selects PROGRAM 6.
Selects the 2-pole mode, refer to paragraph
2.9 for more information concerning front
panel programs.
Programs channel 1 as the first channel.
Programs 25 as the last channel.
Programs the interval time for three seconds.
Turns on the CHANNEL LED, selects the
channel mode for display and resets the
instrument to the first channel.
Turns on the CONTINUOUS LED and selects
the continuous scan mode.
Initiates the continuous scan mode sequence.
2-12