DayTronic System 10 User Manual Book Download

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Since the equivalent input is here expressed as a percentage of full-scale output, you
must multiply it by the rated full-scale capacity of the transducer, in order to determine
the actual input simulated by the shunt.

Shunt calibration is an easier though generally less accurate technique then two-point
(deadweight) calibration. It is useful, however, when overall “deadweighting” is impos-
sible or inconvenient, and is good for an accuracy of about 0.2% (depending, of
course, on the accuracy of the specified equivalent input, and on the resistor/bridge
tolerance and temperature).

The 10A72-2C is equipped with a 100-k

Ω

, 0.1% calibration resistor for each active

channel. These resistors are located on turret terminals at the rear of the card (see
Fig. 4). You may, if you wish, replace each channel’s installed 100K shunt resistor with
a resistor of another value (strain-gage transducer manufacturers often supply such
resistors with their instruments).

In System 10, a strain gage channel’s shunt resistor may be switched in and out by
means of the

SHUNT CALIBRATE—POSITIVE (SHP)

SHUNT CALIBRATE—NEGA-

TIVE (SHN)

command. A

RESUME (RSM)

command should then be applied to

remove the shunt and resume normal channel measurement. Since these are “run-
time” commands, the mainframe’s

EEPROM Write Protect Switch

need not be on

for them to be effective. See Manual Section 1.G.6 for general instructions regarding
the “SHUNT CALIBRATION” technique in System 10.

NOTE:

Per-channel shunt calibration for the 10A72-2C can be “remotely” controlled, if

desired, as an alternative to using the software “SHUNT CALIBRATE” commands pro-
vided by the system. This remote calibration control is accomplished by means of
logic-level inputs to the 10A72-2C card. The relevant connections are given in Fig. 5.

Fig. 5(a) shows how the “CALIBRATE POSITIVE” and “CALIBRATE NEGATIVE” com-
mands can be independely applied to either active 10A72-2C channel, without the
need of an external logic reference supply.

Closing the switch in Fig. 5(a) to contact point “A” will produce a Logic 0 level at Pin D
(“NOT +CALIBRATE”). Since this is a negative-true logic line, the Logic 0 input will acti-
vate the “+CALIBRATE” condition of the channel. That is, it will switch in the channel’s
shunt resistor for a positive up-scale reading. Opening the switch to disconnect the
“NOT +CALIBRATE” line from SIGNAL COMMON will then return the channel to the
“NO +CALIBRATE” condition.

Similarly, closing the switch to contact point “B” will produce a Logic 0 level at Pin E
(“NOT –CALIBRATE”), thereby switching in the channel’s shunt resistor for a negative
up-scale reading. Opening the switch to disconnect the “NOT –CALIBRATE” line from
SIGNAL COMMON will then return the channel to the “NO –CALIBRATE” condition.

You may also use active TTL logic, as illustrated in Fig. 5(b), to produce the “+CALI-
BRATE” or “–CALIBRATE” condition for either 10A72-2C channel.

DayTronic System 10, User Manual Book

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