4-20mA Loop-Powered Isolators, 2-Wire

Models get power from the 4-20mA output or input loop (sinks or sources current). Typical uses are as a current repeater or to drive resistive loads. 651T and 250T models are ideal for applications that require an isolator with a power supply in series with the output signal. Power is obtained from the output loop. The isolator must control current draw from the power supply in the output loop which is the 4-20mA signal. Since output and power share the same two wires, this type of isolator can be placed anywhere between the field sensing device and the PLC/DCS or monitoring device. Usually, the isolator is located close to the field device. Since both the input and output signal are 4-20mA, location of the device is not critical. 670T and 270i models are useful when adding and isolating a monitoring instrument to an existing current loop. When adding a field device such as a recorder or display, no additional power source is required for the added loop or for the isolator. The isolator's output is powered by the input loop power and drives passive loads only.

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    TT236: Current / milliVolt Input Two-Wire Transmitter

    • Multi-range ±20mA or ±500mV input
    • 4-20mA ouput (sink/source)
    • 12-32 V DC loop/local power
    The TT236 model is a space-saving two-wire transmitter that isolates and converts a DC current or low voltage input to a proportional 4-20mA control signal. A single unit supports both voltage and current input for extra flexibility. Power is received from the output loop current or a DC supply when using a three-wire connection. Click here to watch a short AcroMaggie video highlighting the TT230 Series.
    $195
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    DT236: Current / milliVolt Input Two-Wire Dual Transmitter

    •  Dual channels
    •  ±20mA, ±500mV inputs
    • 4-20mA outputs (sink/source)
    • 7-32V DC loop power
    The DT236 model is a dual two-wire transmitter that isolates and converts DC current or low voltage inputs to proportional 4-20mA control signals. Power is received from the output loop current or a DC supply when using a three-wire connection. Click here to watch a short video highlighting the features of the DT236.  
    $270
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    VPM2000 Series: Loop-Powered Isolator / Alarm with Display

    • Loop-powered Process Meter
    • 4-20mA input/output
    • Solid-state relays
    • Non-incendive, intrinsically safe
    These loop-powered 1/8 DIN digital panel meters provide a convenient and informative display of any 4-20mA signal. A dual line display shows the process value on the top line and the units or a tag on the bottom line. Alternatively, you can display the input in one scale on the top line (e.g. height) and another scale on the bottom (e.g. volume). Click here to watch a short video highlighting the VPM2000 Series.      
    $205 – $495
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    651T, 652T: Multi-Channel, Two-Wire Isolators

    • DC current input
    • Single/dual-channel DC-powered isolators
    • Signal splitter
    These units receive 4-20mA process current inputs and provide isolated 4-20mA output signals. Each channel operates independently and is isolated from the others to prevent interaction between channels.
    $195 – $285
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    671T, 672T, 674T: Multi-Channel, Two-Wire Isolators

    • DC current input
    • Single, dual, or quad I/O loop-powered isolators
    These units receive 4-20mA process current inputs and provide isolated 4-20mA output signals. Power is derived from the input signal current. Each channel operates independently and is isolated from the others to prevent interaction between channels.
    $195 – $375
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    250T-DC, 350T-DC, 450T-DC: Analog Transmitter; AC-, DC- or Loop-Powered, DIN Rail-Mount

    • DC voltage or DC current input
    • DC voltage or DC current output
    • Loop or DC or AC power
    • Excellent accuracy and stability ensure reliable measurements in harsh industrial environments. Input isolated from output/power
    $465 – $510
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    270i: Input Loop-Power Isolator

    • 4-20mA DC input
    • 4-20mA DC output
    • 12 to 50V DC @ 20mA (loop-powered)
    • 1500V AC peak isolation DC prevents ground loops
    The 270i accepts a process current input and provides an isolated 4 to 20mA process current output signal. Power is received from the input signal current.
    $510 – $800
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4-20mA Signal Isolators Continued

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Signal Isolators For Signal Conditioning

Acromag support is here to help you choose a signal isolator. Many times choosing the right isolator requires more than just comparing the number of channel and the cost per point.

Here are a few resources that might help you choose a 4-20mA isolator

Some signal isolators are ideal for applications that require an isolator with a power supply in series with the output signal. Power is obtained from the output loop. The isolator must control current draw from the power supply in the output loop which is the 4-20mA signal. Since output and power share the same two wires, this type of isolator can be placed anywhere between the field sensing device and the PLC/DCS or monitoring device. Usually, the isolator is located close to the field device. Since both the input and output signal are 4-20mA, location of the device is not critical.

Other signal isolators are useful when adding and isolating a monitoring instrument to an existing current loop. When adding a field device such as a recorder or display, no additional power source is required for the added loop or for the isolator. The isolator's output is powered by the input loop power and drives passive loads only.