103
External Control Lines
31
31.12 NONSTANDARD RX (PIN 12) AND NONSTANDARD TX (PIN 13)
These two pins allow digital communications with the meter using 5 V CMOS logic levels and
RS-232 protocols and format. This access is normally reserved for specialized equipment com -
mu ni ca tion in a calibration lab or at the factory.
31.13 NO CONNECTION (PIN 14)
31.14 +V EXT (PIN 15)
This is the pin on which to bring in isolated external 5 to 30 V to power the snubbing diodes of
the four setpoint/alarm open-col lec tor transistors.
31.15 SP1 (PIN 16)
The open-collector of the first setpoint transistor (can carry 150 mA).
31.16 SP2 (PIN 17)
The open-collector of the second setpoint transistor (can carry 150 mA).
31.17 AL1 (PIN 18)
The open-collector of the third setpoint (first alarm) transistor (can carry 150 mA).
31.18 AL2 (PIN 19)
The open-collector of the fourth setpoint (second alarm) transistor (can carry 150 mA).
31.19 RTN EXT (PIN 20)
This is the return to the external ground (P2-20) of the external power for the setpoint transistors
and snubbing diodes brought in on P2-15, 16, 17, 18 and 19. Figure 30-2 shows an example of
a circuit using an external relay with SP1 (Setpoint 1). If a solid state relay is used, delete
connection to Pin 15.
Figure 30-2 For Setpoint Transistors
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