Laurel Electronics Laureate RTD Temperature Panel Meter-Controller - Manual (Page 3)

LAUREL ELECTRONICS INC., 3183-G Airway Ave., Costa Mesa, CA 92626, USA • Tel 714-434-6131 • www.laurels.com 3
RTD Connections with Excitation & Lead Compensation
In 4-wire hookup, different pairs of leads are used to apply the
excitation current and sense the voltage drop across the RTD,
so that the IR drop across the excitation leads is not a factor.
In 3-wire hookup, the meter senses the combined voltage drop
across the RTD plus two excitation leads. It also senses the
voltage drop across one excitation lead, and then subtracts twice
this voltage from the combined total. This technique effectively
subtracts all lead resistance and compensates for ambient
temperature changes if the two excitation leads are identical.
In 2-wire hookup, the meter senses the combined voltage drop
across the RTD and both lead wires. The voltage drop across the
lead wires can be measured by shorting out the RTD during meter
setup, and this voltage is then automatically subtracted from the
combined total. However, changing resistance of the lead wires
due to ambient temperature changes will not be compensated.
RTD hookup can be via 2, 3 or 4 wires to the J5 connector. The meter applies an
excitation current of 256 µA (Pt100 and Ni120) or 5 mA (Cu10).
Application Examples
Operation as a 4-20 mA Transmitter
With the optional analog output board, Laureate tempe-
rature meters can serve as superb, isolated 4-20 mA
transmitters. The analog output is scaled to the display,
which is linearized to °C or °F and is exceptionally
accurate. The analog output further tracks the high read
rate of the meter, at up to 60 readings per second at 60 Hz
power. Fast update rates are beneficial in many closed-
loop and PID control applications.
Operation as a Fast Controller
With the dual contact relay or dual solid state relay output
board options, Laureate temperature meters can serve as
extremely fast and accurate ON/OFF controllers for
closed-loop temperature control. Multiple setpoint
operating modes are individually selectable for each relay,
as explained in the dual-setpoint controller section. Relay
duty cycles and chatter can be minimized with
programmable hysteresis and time delays. High duty
cycles and extremely fast response times are possible with
the solid state relay, which has a typical response time of
only 17 ms.
Operation as a Supervisory Monitor
By using the optional dual contact relay or dual solid state
relay output options, Laureate temperature meters can
monitor processes and provide alarms or shutoffs when
these processes exceed normal limits. A band deviation
operating mode can be selected for each relay, where an
alarm is generated whenever the reading is a selected
number of counts above or below the setpoint. Relay
operation can be selected as latching or non-latching.
When an alarm or shutdown condition is reached, a
latched output will remain in the alarm condition until it is
reset by a front panel pushbutton, via the serial interface,
or via the rear connector.