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SL340 Universal Transmitter

SL340 Universal Transmitter

Smart Line is a new series of signal conditioning modules with the following design philosophy

  • Smaller case style.

  • Has a wide range ac/dc power supply.

  • Capable of changing ranges and settings without using test equipment or opening the case.

  • Simple setup and verification process.

  • No trim pots.

  • Real time display input and output values in SL300 programmer.

  • See standard SL transmitter features below.

Smart Selection

Item Available Description
SL303-01 In stock SL Series USB Isolator
SL332-20 In stock Signal Isolator with 10-60Vdc / 16-42V 50/60Hz power supply
SL332-10 In stock Signal Isolator with 80-300Vdc / 80-280Vac 50/60Hz power supply
SL335-20 In stock Signal Splitter with 10-60Vdc / 16-42V 50/60Hz power supply
SL339-20 In stock A cheaper to purchase SL332-20 with more SL300 programming options. (10-60Vdc / 16-42V 50/60Hz power supply)
SL340-20 In stock Universal Transmitter with 10-60Vdc / 16-42V 50/60Hz power supply
SL340-10 In stock Universal Transmitter with 80-300Vdc / 80-280V 50/60Hz power supply
SL350-20 Coming Pulse Frequency Transmitter with 10-60Vdc / 16-42V 50/60Hz power supply
SL300 Icon

Standard SL Transmitter Features

All SL series transmitters now share an advanced set of output features. You may only need one of the features 5% of the time but they are there ready to implement without having to order a different module with special functionality.

Input Linearisation.
The shape of the output response can be customised to compensate for a system with a non liner response.

User Engineering Units and Scaling.
This enables the SL303 software to display input in process units.

Reverse and Direct Action.
Is sometimes require the output to reduce when the the input measurement rises.

Signal limiting.
Enable a linear response between the high and low points beyond which the output will remain the same.

20 character name.
The names is stored in the module and is also used as a file name whan backing up programs on a PC.

The SL300 PC Programmer

This free tool is upgraded with each release of a SL series module. More information on the SL300 PC Programmer is available here.

When used with the SL332/SL335 it can set functions that are not available using the top mounted switches. The SL300 Programmer can read and program all parameters for the entire range of Smart Line signal conditioners.

SL303 USB Connector

The SL303 replaces the COA703 for SL series applications. No more clumsy wires dangling about, no more windows hardware detection problems.

The free revised SL300 software makes programming SL modules easy.

The SL303 is an SL Series USB Isolator which provides galvanic isolation between an SL series signal conditioning module and the USB port on your PC.

Many of you have purchased the SL332 and SL335 modules with switches to set the input and output. Did you know that both of these modules have a user switch position were SL300 software will extended capabilities far beyond other isolators in the same price range.

New SL303

New SL303

The SL340 must be programmed with the SL303 to be programmed as a mV transmitter, Resistance Transmitter, Standard or differential input, Thermocouple Transmitter, Potentiometer Transmitter, RTD Transmitter or Strain Gauge Transmitter.

The SL339 is a SL332 without the top mounted switches.

Ask about getting a free SL303 when purchasing 10 or more SL339 or SL340 modules of the same type at one time.

SL332 Signal Isolator

The SL332 is a field configurable isolating converter providing true 3-way galvanic isolation up to 2500Vrms for standard process signals.

Input and output range are set using two 16 position encoder switches that are accessed under a door flap mounted on the front of the module.

Input and output switch settings

IP Input Switch OP Output Switch
1 0…1mA 1 0…1mA
2 0…10mA 2 0…10mA
3 0…20mA 3 0…20mA
4 4…20mA 4 4…20mA
5 0…50mA 5 0…1V
6 0…1V 6 0…2V
7 0…2V 7 0…5V
8 0…5V 8 1…5V
9 1…5V 9 0…10V
A 0…10V A 2…10V
B 2…10V B 0…20V
C 0…20V
D 0…50V
E 0…100V
F 0…200V
SI132 Set Switches

SL335 Signal Splitter

The SL335 is a field configurable isolating converter/splitter providing true 4-way galvanic isolation up to 1800Vrms for standard process signals. On standard models are 3 x 16 position encoder switches under a door flap to set input and output ranges.

Input and output switch settings

IP Input Switch OP Output 1 and 2 Switch
1 0…10mA 1 0…10mA
2 0…20mA 2 0…20mA
3 4…20mA 3 4…20mA
4 4…20mA LP 4 0…1V
5 0…1V 5 0…2V
6 0…2V 6 0…5V
7 0…5V 7 1…5V
8 1…5V 8 0…10V
9 0…10V 9 2…10V
A 2…10V A 0…20V
B 0…20V
SL335 Switch Setting

SL339 A cheaper isolator with more features.

The SL339-20 is essentially a SL332-22 without the range selection switches fitted. The unit is configured using the SL300 software with no compromises on measurement accuracy and speed.

The SL339-20 packs advanced custom linearisation, signal limiting and direct reverse action into a thin 12.4mm case.

Ask about getting a free SL303 USB Connector when purchasing 10 or more SL339 Signal Isolator modules at one time.

SL339 Program

SL339 Program

SL340 A Better Universal Isolator

The SL340 is the next generation of Universal Transmitter providing true 3-way galvanic isolation up to 2500Vrms for the following input types;

  • mV
  • Position / Slide wire
  • Potentiometer
  • Resistance
  • RTD
  • Strain Gauge
  • Thermocouple
SL340 Supports Many Probes

SL340 Supports Many Probes

Input and output are set using the SL300 programmer connected to a PC USB via the COA703 interface. The connection socked is accessed under a door flap on the front of the module.


Why is SL340 better?


Back in 1999 APCS invented the term Universal Signal Conditioner with the USC701. The unit was designed to replace all other transmitter types so a company could have one unit on the shelf to that could be programmed for the desired function before fitting.

In the market today there are many isolators that claim to have a universal input and cover many mV and temperature ranges.

In many cases these units work well on the specified ranges but when customising the ranges they may suffer from reduced range within the analogue to digital converter on the input or reduced use of the digital to analogue converter on the output. As a result the quoted accuracy will be reduced.

The SL340 has not been designed to replace the USC701. Today’s market requires cheaper isolators and converters that use less power and space. The SL340 represents what the market wants at a completive price.

The SL340 with only four input terminals supports Thermocouple, RTD, Strain Gauge, Resistance, Slide Wire and mV inputs without compromising accuracy.

The programmable input current and voltage sources each have two distinct ranges to maintain accuracy.

The input instrumentation amplifier can be configured as single ended or differential depending on the application. This amplifier has programmable offsets to ensure that the analogue to digital converter is always working over the widest possible range for the user’s input calibration.

Measurements are processed by the input side CPU, this dedicated processing ensures fast conversion to a digital signal that represents the user’s specified input calibration. This digital signal has been corrected to remove standard linearity errors produced by the sensor currently in use (TC, RTD, etc).

A digital data is sent from input to output via an an optical isolator. The output CPU contains an integrated digital to analogue converter and controls the switching of the output range components.

As isolation and output drive method does not rely on pulse width modulation conversion or linear conversion conversion methods no additional linearity and accuracy errors are introduced for a wide range of user defined calibrations.


SL350 Pulse Frequency Transmitter

The SL350 is configured using the SL300 software with no compromises on measurement accuracy and speed.

The SL350 is a pulse to process signal converter providing true 3-way galvanic isolation up to 2500Vrms. A variety of pulse signals and sensor types are supported.

The input span may be 1 pulse every 5 seconds or frequency of 0 to 180kHz. The measurement may be over a narrow range for a deviation applications e.g. 46 to 54Hz.

The AUX sensor supply has both adjustable current and voltage settings reducing hazards in probe wiring and allowing the use of variable resistance sensors. SL350 user software settings include;

  • Standard SL Transmitter features listed above.
  • Frequency measurement range.
  • Input sensor supply.
  • Trigger level setting and capture.
  • Input filter.
SL350 Pulse Frequency Transmitter

SL350 Pulse Frequency Transmitter


Input to output Response Time

Spec Value
Input/Output Response 70msec to 100msec, see below.

When programming you need to specify the frequency range Minimum and Maximum in measure units (Hz or kHz). If MAX <= 150Hz and the input frequency is < 10Hz then the response is one cycle time. When input is 10Hz response is 100mS When input is 1Hz response is 1 second.

SL350 Input Range

SL350 Input Range

Duty cycle and Period

The three wave forms on the right all have the same period, only the duty cycle has changed. When measuring low speed pulses the SL350 is measuring period, it is not a pulse counter.

The SL350 will work on frequencies over the specified 150kHz. This is achieved by using a digital divider on the input signal. The division factor is set from MAX frequency entered during programming. If the MAX programmed as a very high and the input frequency very slow long update times are expected in the first 1% of the measurement range.


5kHz Low Pass Filter

5kHz Square Wave With Filter Applied

Available on all sensor types the low pass filter may be useful in noisy environments. When enabled the rise and fall time is limited to about 100μs in the input amplifier.

If a 50% duty cycle 5kHz square wave (200μs period) were applied the input amplifier will reproduce a signal looking more like saw teeth removing additional higher frequency noise and reducing amplitude by about 30%. Square waves at lower frequencies will appear to have rounded edges.

When using this filter the duty cycle and frequency of the signal must be considered. It is not uncommon for the input pulse to be a fixed ON width and variable OFF width, or a fixed OFF width and variable ON width.


When using this filter the duty cycle and frequency of the signal must be considered. It is not uncommon for the input pulse to be a fixed ON width and variable OFF width, or a fixed OFF width and variable ON width.

There are two pulse input terminals. Terminal 4 LO is used for signals from 50mV to 50Vac, terminal 6 HI is used for signals from 8V to 260Vac. The terminal in use needs to be programmed into the unit.


LO Input and AUX supply

The LO input uses terminals 5, 7 and 8. There are 5 predefined sensor types that use the LO input. These ranges manipulate the AUX supply and trigger point to suit the probe type along with the recommended connection diagram. An additional range “LO- Any Pulse Trigger” has less restrictions to allow you to design your trigger system. All five of the preset ranges may be created using this range

SL350 Input Range

SL350 Input Range

Parameter Spec
LO Input maximum 50Vac
LO Input trigger range 50mV to 6V.
LO Input impedance 100k ohm /1k ohm user setting.
Gain = 1 hysteresis 60mV on trigger > 0.4V
Gain = 5 hysteresis 12mV on trigger < 0.4V
Gain = 10 hysteresis 6mV on trigger < 0.2V
Sensor power supply 0.15 to 15V / 0.2 to 20mA, adjustable

HI - Any Pulse

When using input HI input terminals 6 and 8 are used.

Parameter Spec
HI Input maximum 260Vac
HI Input trigger range 8V to 200V.
HI Input impedance 220k ohm.
Gain = 1 hysteresis 8.8V on trigger > 58.8V
Gain = 5 hysteresis 1.76V on trigger < 58.8V
Gain = 10 hysteresis 0.88V on trigger < 29.4V

If building a mains frequency transducer terminal 8 should be connected to Neutral and terminal 9 to the Active, the SL350 operate safely with the leads reversed however the programming socket and trigger capture button located under the front lid will be at active potential.

SL350 HI Input Connection


The trigger capture button and programming socket are at the same potential as terminal 8. This may be at a dangerous elevated voltage depending on your application.


Trigger level setting and capture.

SL350 Top Controlls

You can specify the trigger point when programming. Many customers are unsure what the trigger point should be. On older modules there is a trigger level pot used to adjust the trigger until the unit starts working. The SL350 can detect the correct trigger level and adjust the input gain and trigger setting to suit connected input pulse/or waveform by pressing the trigger capture button located under the top door.

Press and hold the capture button until the Function LED starts flash at a 1/2 second rate. Release the Trigger Button, the Run LED will stop flashing while the best input trigger for the input signal is determined.

The updated input trigger and input amplifier gain are permanently stored. When initially programming the trigger function is set to “Trigger Capture” or “Trigger tracking”.

Trigger Capture
The stored trigger level input gain is overwritten when top button is pressed.
Trigger Tracking
The stored level is overwritten using the same process as Trigger Capture however the pulse valley and peak levels will be continuously monitored. The trigger is continuously set half way between these levels.
Input Signal with Offset

Input Signal with Offset

Earlier we looked at Input to output Response Time with square waves. The diagrams here show sine and triangle waves but also apply to square waves. From the up down repetition we derive the period of the input signal, this is the primary parameter the SL350 sends to the process output. The best trigger point is half way between the peak and valley which the SL350 continuously determines over a number of periods. The peak and valley values are displayed on the SL300 input display as shown in section Input Display on PC app.

When input pulses derive from proximity sensors the signals are positive square signals. When input pulses derive from magnetic speed sensor the signal is generally sine with an equal positive and negative half. The SL350 only measures and triggers on the positive part of an input signal. In the example shown the valley is 0 and the peak is 1. Automatic trigger level will set the trigger point at 0.5. The trigger should be set while the input is at the lowest piratical speed.

Bipolar Signal Input

Bipolar Signal Input

The trigger should never be set at 0 which is half way between +1 and -1 as when there is no signal applied the background noise will trigger random measurements. The lowest trigger level allow by the software is 50mV. The ‘LO Inductive Speed Sensor’ range defaults the trigger to 150mV.


Input Display on PC app SL300

The SL350 measures frequency / period and converts the measurement into a standard process output. The input pulse valley and peak are also continuously measured for the trigger capture function.

SL350 Display Input

SL350 Display Input

Position Label Meaning
Top left 2.51 measured input in.
. LPM engineering units
Second left T7 Input terminal.
. 900.00-3000.00 MIN - MAX
. Hz Measure units
. Linear Shape.
. 950.22Hz Measurement
Bottom left C:0.9-3_ Eng range.
. LPM Eng units.
. V:0.606 Valley, input min (volts).
. P:5.574 Peak, input max (volts).
. T:3.00 Trigger level (volts).