Model DT335-0700
Dual RTD/Resistance Input Transmitter w/USB
Acromag, Inc. Tel: 248-295-0880
- 7 -
http://www.acromag.com
- 7 -
https://www.acromag.com
Sensor Input Connections
This module supports 2, 3, and 4-
wire input connections from RTD
and resistance sensors. Sensor
wires are wired directly to
transmitter input terminals at TB1
(channel 1) and TB3 (channel 2) at
the bottom of the module (the
spring-loaded DIN clip side), as
shown in the connection drawing
below. Observe proper polarity
when making input connections.
•
Channel inputs are isolated from each other and from each output
.
•
Unit has three operating modes
: You may operate this unit as a dual
transmitter, a single transmitter, or a CH1 signal splitter.
•
Three-wire input connections require one wired jumper to be placed between
input (H) and input (+)
. This jumper routes excitation current from the input
(H) terminal to the input (+) lead of the sensor. Excitation current passes
through the sensor and produces a sensor voltage drop that is measured
differentially between the input ± leads.
•
Two-wire input connections require two wired jumpers to be placed between
input (+) and input (H) and between input (-) and input (L)
. The second
jumper routes the excitation return current from input (-) to the A/D reference
resistance at the input (L) terminal to accomplish ratio-metric conversion of the
sensor signal. Ratio-metric refers to measuring sensor resistance as a ratio of
the reference resistance used to drive the A/D reference, rather than
measuring it using an absolute reference voltage. By using the same excitation
current to excite both the sensor and the A/D reference resistor at the same
time, any changes in excitation current will be immediately reflected in the ADC
reference, resulting in a more accurate and stable measurement.
•
Four-wire input connections use no wired jumpers and eliminate errors
associated with sensor lead-wire resistance.
In a 4-wire connection, the
sensor voltage is measured using a different pair of leads (input ±) than the
ones that carry the sensor excitation current (input H & L), effectively removing
lead-wire IR drop from the sensor measurement by the A/D.
A 3-wire input
connection accomplishes the same thing, but only if the third-wire matches the
input ± wires in diameter, length, and material (and therefore resistance).
