QLS Quad Output 4-20 mA Current Loop Splitter / Retransmitter

Splits 1 input signal into 4 independent 4-20 mA current loops with ± 10V common mode isolation between input & outputs. Priced at only $200 for AC power or $230 for 24 Vdc power.
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Isolating 4-20 mA current loop splitter
Key Features
  • Accepts a 4-20 mA, 1-5V, 0-5V or 0-10V input signal.
  • Drives four (4) independent 4-20 mA outputs proportional to input.
  • Outputs can share a common ground.
  • Grounds of input and outputs can differ up to ±10V.
  • Opening any output loop does not affect other loops.
  • ±10% zero and span fine adjustments for each output loop.
  • Loop current test point for each output, where 200 mV = 20 mA
  • Indicator LED for each connected output.
  • Powered by 85-264 Vac (Model QLS-1) or 10-48 Vdc (Model QLS-2).
  • Powers a 2- or 3-wire input transmitter at 24V with up to 30 mA.
  • 22.5 mm (0.9") wide case snaps to 35 mm DIN rail.
  • Weighs only 159 g (5.6 oz).
Problems with Current Loop Loads in Series

Not so good:  A single 4-20 mA loop from a sensor is connector to a panel meter, a control valve, a recorder and a PLC in series. If the loop opens, all devices in the loop fail.

1. All devices in the loop cannot share a common ground, but must be electrically floating. This is often not possible.
2. When any device in a loop is removed, fails, or if a wiring fault occurs, all other devices in the loop loose their 4-20 mA signal.
3. The transmitter(signal conditioner) voltage compliance limit may be exceeded, since the voltage drops across loads in series are additive.
4. The 4-20 mA signal to each load device cannot be individually adjusted for calibration purposes.
There are not diagnostics for the current to each load.

The Laureate QLS Loop Splitter / Retransmitter Solution

QLS Quad Loop Splitter connections

Much better:  Four independent 4-20 mA loops with ±10V common mode isolation. If any of the
output loops opens, only a single device is affected. The output loops can share a common ground.

1. Sources up to four (4) independently adjustable 4-20 mA outputs from a single input, which can be 4-20 mA, 1-5V, 0-5V or 0-10V, as selected by jumpers.
2. If any device in an output loop is removed from a loop or fails, or if a wiring fault occurs in any loop, the other loops continue to operate properly.
3. The outputs can share a common ground. The input and outputs are mutually isolated to ±10V by means of active circuitry to accommodate differences in local grounds with normal industrial grounding practices.
4. Each loop only drives a single load, thus avoiding voltage compliance problems.
5. ±10% of zero and span adjustment are provided for each output loop to allow for independent loop calibration.
6. Diagnostics for each output loop are provided by a yellow LED lamp to indicate loop continuity and by a test point across a 10Ω series resistor, where 200 mV corresponds to 20 mA. The test point allows a multimeter to measure the loop current without breaking the loop.
Power for the loop splitter can be 85-264 Vac (Model QLS-1) or low voltage 10-48 Vdc or 12-32 Vac (Model QLS-2). An excitation output is provided on the signal input side to drive a 2- or 3-wire transmitter at 24 Vdc and up to 30 mA.
Specifications Back to top
Signal Input
Signal Type
Input Resistance
Transmitter Excitation
4-20 mA, 1-5V, 0-5V, 0-10V (jumper selectable)
50 Ω for 4-20 mA, 412 kΩ for 1-5V, 464 kΩ for 0-5V, 935 kΩ for 0-10V
24 Vdc nominal, 30 mA max
Signal Outputs
Number of Outputs
Signal Type
Zero & Span Adjustments
Signal Isolation
Voltage Compliance
Load Regulation
Zero Tempco
Span Tempco
AC Rejection
Response Speed
Loop Current Sense
Loop Continuity Indication
4-20 mA, sourcing
± 10% for each output with 25-turn potentiometers
± 10V active isolation between input and output grounds
12V (600Ω per loop at 20 mA)
± 0.005% of span from 0Ω to 600Ω
± 0.02% max span error at 23°C
± 0.1 µA/°C typical, ± 0.2 µA/°C max
± 10 ppm/°C (0.16 µA/°C) typical, ± 20 ppm/°C (0.32 µA/°C) max
90 dB from DC to 60 Hz
2 ms risetime, 7 ms settling time to 0.1% of final value
10Ω ± 0.5% series resistor. Generates 200 mV at 20 mA
Yellow LED lamp per loop, brightness proportional to current.
Power Input
Standard Power (QLS-1)
Low Power Option (QLS-2)
Power Frequency
Power Isolation
Power Consumption
Power On Indication
85-264 Vac or 90-300 Vdc (DC operation not ETLapproved)
10-48 Vdc or 12-32 Vac
DC or 47-63 Hz
250V AC working, 1.0 kV AC for 60 sec, 1.7 kV DC for 2 sec
3.5 W max, all loops delivering 20 mA
Green LED lamp
Wire Size
35 mm DIN Rail per EN50 022
22.5 x 103 x 128 mm (0.9" x 4.1" x 5.0") W x H x D
140 g (5 oz)
Detachable plug-in screw-clamp connectors
28-12 AWG, 2.5 sq. mm max
Operating Temperature
Storage Temperature
Relative Humidity
Cooling Required
-40°C to 70°C
-40°C to 85°C
95% at 40°C, non-condensing
Mount units with ventilation holes at top and bottom.
Leave 6 mm (1/4") between units, or force air with a fan.

QLS Pinouts and Theory of Operation

QLS Quad Loop Splitter theory of operation

Galvanic & Active Isolation: A single input current loop is split into four independent output loops I1, I2, I3 and I4 by four current generators. The input and output signals are galvanically isolated from power and earth ground by up to 275 Vac. Active circuitry isolates the input Signal Ground and the four output Local Grounds from each other to a common mode voltage of ±10V, thereby avoiding ground loops. Common mode voltages, labeled CMV1 to CMV4 in the diagram, reflect actual voltage differences between Signal Ground and Local Ground. Such differences can be caused by current flows in the factory.

Floating loads: Any output load R that is floating (not connected to Earth Ground or a Local Ground) can be connected between current output (Pin 1) and current return (Pin 2). Current return is internally tied to Signal Ground, which can be floating or be connected to earth ground.

Grounded loads: Any output load R can be connected to a Local Ground instead of current return. The Local Grounds can each be different, but can only differ from Signal Ground by a safe common mode voltage CMV. Signal Ground should be tied to minimize noise pickup.

Input-output isolation: If a load R is grounded to a Local Ground, the available common mode voltage CMV is limited on the positive side by the unit's internal power supply and on the negative side by the 600 mW power dissipation limit of an output transistor. The above diagram shows allowable CMV as a function of output load resistance R. For example, with a 250Ω load, CMV can range from -13V to +17V. With a 500Ω load, CMV can range from -18V to +12V. The unit will not work correctly if CMV limits are exceeded or the load resistance is greater than 600Ω.

Ordering Guide Back to top
Laureate QLS Quad Output 4-20 mA Loop Splitter / Retransmitter
Click on the radio buttons to build a model number with pricing as shown below.
Please see our explanations and limitations applicable to pricing and online orders Prices shown are in US Dollars and are Laurel's manufacturer's suggested retail price (MSRP) in the USA. Orders are processed manually, not directly by our shopping cart system. You don't have to supply credit card information when placing an online order.

North American Orders. Laurel does not sell factory-direct in the USA or Canada. Online sales orders are filled through distribution. During the ordering process, you will have the chance to select an authorized Laurel distributor, or you can ask Laurel to refer you to a distributor. The distributor will then contact you to quote shipping, tax and duty (where applicable), and arrange for payment.

International Orders. If your ship-to address indicates that you are outside of the USA or Canada and Laurel has a distributor in your country, we will forward your order to that distributor for follow-up. If Laurel does not have a distributor in your country, we will email you an order acknowledgment and a pro forma invoice which states the product price, shipping charges, and wire transfer information, which includes a $25 bank wire transfer fee.

Questions about your order? Please email your distributor or sales@laurels.com

Configured model number QLS-1
Configured price per model $200
Quantity 1
Extended price $200
Quad Isolated Output Loop Splitter Retransmitter, 95-264 Vac or 90-300 Vdc power
Quad Isolated Output Loop Splitter Retransmitter, 10-48 Vdc or 12-32 Vac power

  1. What are key features of model QLS?
    The Laureate QLS is a quad loop splitter / retransmitter which can split one 4-20 mA input current loop into up to four independent 4-20 mA output loops. These are are individually scalable, can share the same ground, or can each each have their own ground. If any of the output loads suffers a failure or is removed, the signals to the other loads are not affected, as would be the case if all loads were in series on the same loop.
  2. How is model QLS mounted?
    The QLS loop splitter has the same case as a Laureate transmitter and snaps into a 35 mm DIN rail like a Laureate transmitter.
  3. How is model QLS powered?
    Power for the loop splitter can be 85-264 Vac (Model QLS-1) or low voltage 10-48 Vdc or 12-32 Vac (Model QLS-2).
  4. Is programming required?
    No programming is required. This is an all-analog product. The signal input (4-20 mA, 1-5V, 0-5V, 0-10V) is selectable via jumpers. Fine adjustment of zero and span of each of the four 4-20 mA analog outputs is via a screwdriver.
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