RTD Temperature Panel Meter / Controller

High accuracy plus linearized transmitter & control outputs

RTD temperature meter by TD Micronic


  • Reads 100Ω platinum, 10Ω copper & 120Ω nickel RTDs
  • 2, 3 or 4-wire connection with lead resistance compensation
  • Selectable 1°, 0.1°, or 0.01° resolution, °C, °F, K or R
  • Up to 60 conversions per second, peak or valley display
  • Universal 85-264 Vac / 90-300 Vdc or 10-48 Vdc / 12-32 Vac power
  • Wide choice of options:
    - 2 or 4 relays, mechanical or solid state (isolated)
    - Analog output, 4-20 mA, 0-10V, or -10V to +10V (isolated)
    - Serial data I/O: Ethernet, USB, RS485, RS232 (isolated)

The RTD meter is factory calibrated for four Resistance Temperature Detector (RTD) types: 100-ohm platinum (Pt100) with DIN alpha of 0.00385, 100-ohm platinum (Pt100) with ANSI alpha of 0.003902, 10-ohm copper with alpha of 0.00427, and 120-ohm nickel with alpha of 0.00672. The entire span of each RTD type is presented in a single range. The RTD type, unit of measure (°C or °F) and resolution (1°, 0.1° or 0.01°) are selectable from the front panel or via the meter's serial interface. Display in Kelvin or Rankin is selected by offsetting the Celsius or Fahrenheit ranges. Typical accuracy is better than ±0.1°C (±0.2°F).

RTD connections can be via 2, 3 or 4 wires. With 3 or 4-wire connections, the meter automatically compensates for changes in lead resistance to the sensor. With 2-wire connection, the meter can measure and then subtract the lead wire resistance.

All ranges for all RTD types are digitally calibrated at the factory, with calibration factors stored in an EEPROM on the signal conditioner board. This allows temperatures sensors and signal conditioner boards to be changed in the field without recalibrating the meter.

Load cell signal conditioner board for TDM digital panel meterHigh read rates at up to 60 or 50 conversions per second while integrating the signal over a full power cycle are provided by Concurrent Slope (US Pat 5,262,780) analog-to-digital conversion. High read rates are ideal for peak or valley capture, real-time computer interface, and control. Peak and valley values are standard. These may be displayed via a front panel pushbutton command or a control signal at the rear connector, or be transmitted as serial data.

Digital filtering is selectable for electrically noisy environments or resolution to 0.01°, including a batch averaging filter and an adaptive moving average filter which provides a choice of 8 time constants from 80 ms to 9.6 s. When a significant change in signal level occurs, that filter adapts by briefly switching to the shortest time to follow the change, then reverts back to the selected time constant. In a selectable Auto filter mode, the filter time constant is automatically selected based on detected signal noise.

Designed for system use. Optional plug-in boards for communications and control include Ethernet and other serial communication boards, dual or quad relay boards, and an isolated analog output board. s may be powered from 85-264 Vac or optionally from 12-32 Vac or 10-48 Vdc. The display is available with red or green LEDs. The 1/8 DIN case meets NEMA 4X (IP65) specifications from the front when panel mounted. Any setup functions and front panel keys can be locked out for simplified usage and security. All power and signal connections are via UL / VDE / CSA rated screw clamp plugs.

RTD Connections with Excitation & Lead Compensation

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).

In 4-wire hookup, different pairs of leads are used to apply the excitation current and sense the voltage drop across the RTD for ratiometric operation, 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.
Alpha R at
R at top
of range
Range Max Error
100Ω 390.48Ω
at 850°C
196 µA -202°C to +850°C
-331°F to +1562°F
±0.03°C ±0.01% of rdg
±0.05°F ±0.01% of rdg
100Ω 394.36Ω
at 850°C
196 µA -202°C to +631°C
-331°F to +1168°F
±0.04°C ±0.01% of rdg
±0.07°F ±0.01% of rdg
0.00672 120Ω 380.31Ω
at 260°C
196 µA -80°C to +260°C
-112°F to +500°F
±0.05°C ±0.01% of rdg
±0.09°F ±0.01% of rdg
0.00427 9.035Ω 19.116Ω
at 260°C
5.0 mA -100°C to +260°C
-148°F to +500°F
±0.05°C ±0.01% of rdg
±0.09°F ±0.01% of rdg
* The applied excitation current is sensed by the meter, which operates in a ratiometric mode and
  automatically compensates for any changes in excitation.
Readout 5 LED digits, 7-segment, 14.2 mm (.56")
Color Red or green LED
Indicators Minus sign, 2 red LED lamps
Calibration, Pt 100 DIN Per IEC 751 (ITS-90)
Calibration, Pt 100 ANSI NIST Monograph 126
Calibration, Ni 120 DIN 43760
Max error at 25°C, Pt100 ±0.04°C (±0.07°F) ±0.01% of reading
Span tempco ±0.003% of reading/°C
Zero tempco ±0.03 deg/deg
Provision for user calibration Multiplier of RTD resistance plus offset in degrees
Connection 2, 3 or 4-wire
Overvoltage protection 125 Vac
Open sensor indication Flashes full-scale
Sensor lead resistance 2-wire, 10 mdeg/Ω/deg up to 10Ω
Tempco per conductor 3 & 4-wire, 10 mdeg/Ω/deg up to 100Ω
A-to-D Conversion
Technique Concurrent Slope (Pat 5,262,780)
A-to-D rate 60/s at 60 Hz, 50/s at 50 Hz
Output update rate 56/s at 60 Hz, 47/s at 50 Hz
Display update rate 3.5/s at 60 Hz, 3/s at 50 Hz
Voltage, standard 85-264 Vac or 90-300 Vdc
Voltage, optional 12-32 Vac or 10-48 Vdc
Frequency DC or 47-63 Hz
Power  consumption (typ. base meter) 1.2W @ 120Vac, 1.5W @ 240Vac, 1.3W @ 10Vdc, 1.4W @ 20Vdc,
1.55W @ 30Vdc, 1.8W @ 40Vdc, 2.15W @ 48Vdc
Power Isolation 250V rms working, 2.3 kV rms per 1 min test
Ratiometric operation Automatically compensates for changes in excitation level.
Analog Output (optional)
Output levels 4-20 mA, 0-20 mA, 0-10V, -10 to +10V (jumper selectable)
Current compliance 2 mA at 10V ( > 5 kΩ load)
Voltage compliance 12V at 20 mA (< 60Ω load)
Scaling Zero and full scale adjustable from -99999 to +99999
Resolution 16 bits (0.0015% of full scale)
Isolation 250V rms working, 2.3 kV rms per 1 min test
Relay Outputs (optional)
Relay types 2 Form C contact relays or 4 Form A contact relays (NO) 2 or 4 Form A, AC/DC solid state relays (NO)
Current tatings 8A at 250 Vac or 24 Vdc for contact relays 120 mA at 140 Vac or 180 Vdc for solid state relays
Output common Isolated commons for dual relays or each pair of quad relays
Isolation 250V rms working, 2.3 kV rms per 1 min tes
Serial Data I/O (optional)
Board selections RS232, RS485 (dual RJ11 or RJ45 connectors), USB, Ethernet, USB-to-RS485 converter, Ethernet-to-RS485 converter
Protocols Modbus RTU, Modbus ASCII, Modbus TCP (Ethernet), TDM ASCII
Data rates 300 to 19200 baud
Digital addresses 247 (Modbus), 31 (TDM ASCII),
Isolation 250V rms working, 2.3 kV rms per 1 min test
Operating temperature 0°C to 55°C
Storage temperature. -40°C to 85°C
Relative humidity 95% at 40°C, non-condensing
Protection NEMA-4X (IP-65) when panel mounted

Application Examples

Linearized 4-20 mA transmitter output of  temperature panel meter

Operation as a 4-20 mA Transmitter

With the optional analog output board, RTD temperature 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.

Temperature controller operation of  temperature panel meter Combined temperature controller and 4-20 mA transmitter operation of  temperature panel meter

Operation as a Fast Controller

By using the optional dual contact relay or dual solid state relay output options, 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.

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