HF scientific 19998 Triple Validation Turbidimeter - 0-100 NTU - Manual (Page 13)

TVT 1 (5/02) 7
Rev. 2.6 (.pdf)
Pin 1 = 15 –18 VDC (Not Polarity Sensitive)
Pin 2 = 15 –18 VDC (Not Polarity Sensitive)
Pin 3 = No Connection
Pin 4 = No Connection
Please observe safe wiring practices. It is recommended that a circuit breaker or switch
be placed prior to the power connection to the TVT to allow for service.
Relays: The instrument is pre-wired with a 1.8m (6 ft.) long 9-wire relay cable. Please
Note that the alarms are fail-safe in the manner that the relays are normally actuated and a
loss of power will change the relays’ state. The color code is shown below:
Orange
= Alarm 1 Normally Closed (open on alarm or on loss of power)
Yellow = Alarm 1 Common
Blue = Alarm 1 Normally Open (closed on alarm or loss of power)
Green = Alarm 2 Normally Closed (open on alarm or on loss of power)
Violet = Alarm 2 Common
Grey = Alarm 2 Normally Open (closed on alarm or loss of power)
Black = Sensor Alarm Normally Closed (open on alarm or on loss of
power)
Brown = Sensor Alarm Common
Red = Sensor Alarm Normally Open (closed on alarm or loss of power)
The Alarm 1 and Alarm 2 relays are mechanical relays rated at 240 VAC 2A. There is
also a Sensor Alarm relay that is a mechanical relay rated at 24 VDC 1A. Please note that
the relays are labeled NO (Normally Open), NC (Normally Closed) and C (Common). As
these alarms are configured fail-safe, the normal condition is with power applied and in a
non-alarm condition. Operation of these alarms is covered in section 8.5 Configuring the
Alarms
Communication Signals: Depending on the option that was purchased with the
instrument, several outputs come pre-wired to the instrument with a 1.8m (6 ft.) long
cable. The connections are shown below:
Brown
= RS 485 A
Red = RS 485 B
Orange = RS 485 Shield
Yellow = Flow Switch (Optional Accessory)
Green = Flow Switch (Optional Accessory)
Blue = 4-20 mA Positive Connection
Black = 4-20 mA Negative Connection
RS 485: The RS485 half-duplex (2-wire) digital interface option operates with
differential levels that are not susceptible to electrical interferences. This is why cable
lengths up to 3000 ft can be implemented. The last device on every bus must be
terminated with a 120 ohm resistor to eliminate the possibilities of signal reflection on the
line. Do not run RS 485 cables in the same conduit as power.
Ensure each instrument is not powered when connecting the RS 485 line. Connecting an
instrument while powered may cause the instrument to unnecessarily reset and proceed
through the power on checks.