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300544655_002_C1 - 11/2016 - © Leybold
4.2 Setpoint relays
The TTR 101 N THERMOVAC transmitters have up to three mechanical relays that can be used for controlling
external process equipment. The relays have closing and breaking contacts and the contacts are rated 30 VDC, 1 A,
resistive load. For the setup of the setpoints, refer to chapter 6.
Inductive relay load
Special precautions should be taken when driving inductive loads with the relay contact. When an inductive load
like a solenoid is energized, the in-rush current is significant higher than the regular load current. In-rush currents
exceeding the relay contact rating can cause reduction of relay contact life time or contact reliability.
When a solenoid is de-energized, the collapsing magnetic field can cause significant voltage spikes. These spikes
can couple capacitively from cable to cable and interfere with measuring electronics or transmitter signal.
An arc suppression network, as shown schematically to the right, is
recommended. The values of the capacitance C and the resistance R can
be calculated by the following equations:
C = I
2
/(1 x 10
7
)
R = E/ I
a
where:
C is in Farads. R is in ohms
I is DC or AC
peak
load current in amperes. E is DC or AC
peak
source voltage in volts
a = 1 + (50/ E)
Note that R
min
= 0.5 Ω and C
min
= 1×10
-9
F, D is a fast transient suppression diode.
Setpoint functionality
The set point relays can be activated either above or below the set point values. The graphs below show the
different relays stages in either below or above configuration. The NC contact will always be closed in case of
power failure.
Driving inductive loads via the setpoint relay contacts requires de-energizing spike protection.
Inadequate protection can cause permanent damage to the transmitter or interfere with the analog
output signal.
Always ensure that inductive in-rush currents do not exceed relay contact rating.
When using the setpoint relay to control process equipment always take appropriate precautions to
prevent system damage in case of transmitter power failure. The NC contact will be closed in case
of transmitter power failure.
Critical
!
Critical
!
Summary of Contents for THERMOVAC TTR 101 N
Page 10: ...10 300544655_002_C1 11 2016 Leybold 2 2 Dimensions mm P N 230702V02 P N 230354V02 to 230356V2...
Page 39: ...39 300544655_002_C1 11 2016 Leybold...
Page 40: ...40 300544655_002 10 2015 Leybold Declaration of Conformity...
Page 41: ...41 300544655_002 10 2015 Leybold Notes...
Page 42: ...42 300544655_002 10 2015 Leybold Sales and Service...
