MODEL 171
“P”
r----- --r----- ---
1
1
j 1
j 1
lNP"T,
;i
-1
1 *v,x,*V,,,
I R
R
-I
' i
' i
STROBEa-t"
Y-
i
+‘
< OUTPUT
OUTPUT
I
L-J I
I
------i-m -I
------i-m-
*
COM
FIGURE 6. OUtpUt Buffer stage.
2. Coune Period. During the "COUNT" period,
the integrating amplifier is driven to zero by
a discharge voltage, with the analog signal re-
moved from the amplifier. The "COUNT INTERVAL"
represenes the actual count time for the integrat-
ing amplifier to reach a zero crossing from the
original level of the applied signal. Thus, this
interval is proportional to fhe analog input sig-
"al and may be from 0 LO 200 milliseconds in d"P
ation. For a 100% overrange signal, this interval
would rhen be at its maximum value of 200 milli-
SW""dS.
3. Zero Period. During the "ZERO" period, the
analog amplifier is zeroed, and the decade cou"fers
are reset &xTor co a new c"""ersi"n cycle.
f. Timing outputs and Remote Controls.
(Refer to
Table 2-7 and Figure 7). The Model 1712 Digital
output provkles various timing outputs and remote
controls co regulate the transfer of data from the
Model 171 DMM to a particular digital acquisition
system.
1. Clock. The "Clock" timing output provides
100 kHz pulses which serve as a reference frequency
for direct binary outputs when used in conjunction
with the "Count Interval" output.
2. count Interval. The "Count Interval" timing
output (see Paragraph 2%9e2, may be used wieh an
exCer"a1 binary ripple counter and gate to obtain
a reading directly in binary form.
3. Flag (F-zg). The "Flag" output 1s a negative-
go*ng logic state "1" that appears for a 300~milli-
seco"d interval out of a total conversion eime of
500 milliseconds. No change in digital output is
made during this interval. The "FTg" output is
a positive-going logic state “0” and is available
for use with digital equipment that will not accepr
the negative-going "Flag" output.
4. Strobe. The "Strobe" remote control consists
of 8 lines to paIlif word serializing in 4-hit in-
*
CrenleneG or multiples thereof. A" open circuit
inhibits the controlled output lines from conduct-
ing (closure enables conduction). This allows 8,
12, or 16-hit compueers to be easily ineerfaced
with the Model 1712 without the need of a" Fnter-
mediate register. Also, fhese "Strobe" controls
allow the user to connect together the data outputs
Of two or more i"sCr"me"ts. Each instrument CB"
then be individually interrogated, without disturb-
ing the ocher instruments, by simply grounding the
strobe lines of the particular instrument of inter-
est. when not using rhe strobe feature of the
1712, keep all strobe lines closed to common
(ground).
5. Hold. The "Hold" remote control, by closure,
retains the result of the last A-to-D conversion
in both the 1712 output and the display.
6. Hold 112and Trigger. Closure of the "Hold 112"
remote control halts conversions at the end of the
present conversion, holding the conversion result
in both the 1712 output and the display. The
'Trigger" remote concro1 operates only When "Hold
i/Z" is also in use. The release-edge of B pulsed
closure initiates one conversion, during which time
the signal is averaged for a x30-millisecond period
starting 100 milliseconds after the release of
either fhe "Trigger" or "Hold ,/Z". Minimum "Trigger"
closure time is one microsecond. The high or open
state of the "Trigger" must be + 2 to + 5 volts.
Both "liold 112" and 'Trigger" must be left in the
open stafe when not in use. "se Model 1712 oucwt
pin number 27 (Common) as ground far all closures.
7. Flag @lag) Reset. The "Flag (Flag) Reset"
remote control allows for early reset Of the Flag
(FTg) while operating the Model 1712 in any mode.
This control can be used whenever the digital r&d-
0°C equipment connected to elle 1712 operates faster
than the time the Flag (Flag) is~active (300 milli-
seconds). For example, activation of the Flag
-
(Flag) can tell a computer to take data from the
Model 1712 and r-u" a program which may only take
20 milliseconds. At the end of the program, the
-
computer still sees clle Flag (Flag) and needlessly
~-e--runs ehe program with duplicate data. By using
the "Flag @lag) Reset" control, computer running-
time is minimized and data-taking time is not lost.
g. ~umary of Digital O~twts and Conrrols. The
basic rermi""l"gy and some pin-to-function relation-
ships of the outputs and controls of the Model 1712
will now be discussed. Refer to Table 2-7.
1. Digital output Codes. The digital OUtpUt
code for the Model 1712 is 8-4-2-1 Binary Coded
Decimal (BCD). Each digit of a reading is re-
presented at the BCD output by a four-bit binary
code. The "units" digit of a reading is repre-
sented by the output of pin numbers 1,2,3 and 4.
The "tens I' digit of a reading is represented by
the output of pin numbers 5.6.7, and 8. The
"hundreds" digit is represented by the output of
pin numbers 9,10,11, and 12. The "thousands" digit
is represented by the output of pi" numbers 13,14,
15, and 16. The "ova-range" digit is represenzed
by the output of pin number 17. Thus, in BCD
language, each digit of 4-112 digit display of the
Model 171 is represented for display by a printer
773