www.miinet.com
Moore Industries-International, Inc.
- 13 -
User’s Manual
238-741-00K
May 2019
Programmable Smart HART Temperature Transmitter
THZ
3
/ TDZ
3
SECTION 1
Broken Wire Detection
During operation, the THZ
3
and TDZ
3
send random microamp pulses through input wiring to
check for broken wiring or a burned out sensor. By default the broken wire detection is always
enabled, and this feature is essential to ensure that dangerous failure of the sensor or signal
input is detected by the THZ
3
and TDZ
3
and consequently alarmed.
If the THZ
3
/TDZ
3
detects a broken wire or burned out sensor during operation, the transmitter
sets the output upscale or downscale to warn of trouble. The transmitter is able to identify
sensor wire(s) causing the problem and indicate the fault as a message to the HART Handheld/
FDT HOST, TDZ
3
display and by setting a HART status bit. Specific error messages eliminate
the work of removing the sensor or checking all lead wires to diagnose a problem. This feature
is especially valuable during startup.
Additionally the THZ
3
and TDZ
3
have another feature referred to as BW (Broken Wire) Holdoff
Time. This allows users to add an additional time delay before the broken wire diagnostic alert
is reported. When enabled, a Broken Wire delay of 0-60 seconds can be set. This feature
prevents the transmitter from going into a fault state when intermittent high levels, or spikes, of
extraneous plant noise is conducted onto the sensor leads.
To setup Corrosion Detection, the user captures the nominal sensor resistance value and sets
the Warning and Alarm limits. These can be set at different levels or the same level for both.
See chart below for clarification.
Selecting Warning will set a fault message on the TDZ3 display and send a HART message to
any HART Handheld or HART monitoring HOST. In addition an alert will be sent to any FDT
host that is communicating with the transmitter. Selecting Alarm will also drive the Analog output
to Fail Mode if the sensor is assigned to the PV. If the unit is in backup mode, and the primary
sensor has a corrosion alarm, the PV will switch to the backup sensor.
2ohms
40ohms
35ohms
WARNING
RTD WIRE
RESISTANCE
RTD
Wi
re
Resistanc
e
T/C Circuit Resistanc
e
CAPTURED
VALUE
ALARM
2ohms
35ohms
Different Values
Same Values
RTD WIRE
RESISTANCE
CAPTURED
VALUE
WARNING
& ALARM
200ohms
4,000ohms
3,500ohms
3,500ohms
WARNING
T/C CIRCUIT
RESISTANCE
CAPTURED
VALUE
ALARM
200ohms
Different Values
Same Values
T/C CIRCUIT
RESISTANCE
CAPTURED
VALUE
WARNING
& ALARM
