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MEDACS Modules

  • Smart Configurable
  • Single or Dual Channel
  • Galvanic Isolation
  • Universal or Frequency Input
  • mA and Relay Output
  • Remote I/O via RS485
  • OPC Compliant
  • Easily Customized via TFML
  • Unique "Bus Jumper" System


The MEDACS II is a totally new concept in DIN rail signal conditioners.  It consists of a family of modules that allow the user to select the input and output. Two basic input modules are available. The 2100 and 2200 series universal input units accept RTDs, TC, mA and DC volts. The 2300 and 2400 series accept frequency inputs. Output options include isolated 4-20 mA, single SPDT relay and dual N/C relays, in various combinations.

All units have RS485 Modbus serial communication which is used in conjunction with our M-Config software to configure the modules. The M-Config software is loaded into a PC and communication to the MEDACS is established through a comms port on the PC. This usually requires an RS232 to RS485 converter that is optionally available. The software program is very easy to use and intuitive using pull down menus and dialog boxes. Single channel units have a built-in keypad and digital display that can also be used to configure the units. More than 50 points of linearization can be programmed into the modules either via RS485 or by using the keypad on the single channel modules. Polynomials can also be programmed into the conditioners using RS485. In addition more complex functions can be programmed using our TFML.

About TFML
In addition to the normal range of functions incorporated within the MEDACS instruments, there is the ability to program the software in order to customize its function. The normal operation of a standard transmitter is as indicated below. The electrical input is processed to linearize and condition the sensor value. The value is used to create an output. The relationship between process input and output is referred to as the transfer function. In this case it is a simple relationship but more complex relationships are often required.


> TO >


If the relationship between input and output can be broken, a programmable module can be inserted and be used to define a new transfer function as shown below.


> TO >


> TO >


A transfer function is defined and a program written for it. These program modules can either be obtained pre-written for standard features such as A-B, or written for a specific requirement. These pre-written functions are available from a library of modules on our TFML web page, hence the name Transfer Function Module Library.
TFMLs Currently Available
  • Rate of change limiter
  • Peak Pick/Hold
  • Valley Pick/Hold
  • (A+B)/2
  • A-B
  • Totalizer with relay pulse output
  • PID function block
  • Sensor Validation
    Please contact the Sales Office for details of other custom macros. New ones are being added all the time.
About Remote I/O
Modbus is a master-Slave protocol. This means all communications are initiated by the Master device (ex. Computer, PLC, DCS) and in general the Master communicates with one Slave device (ex. MEDACS II) at a time.

The RS485 mode determines the way that the network is connected together. The MEDACS II can be configured in either the 2-wire or 4-wire mode shown above. The 2-wire arrangement has both transmit and receive signals. In comparison, the 2-wire mode makes the most efficient use of wire and connections while the 4-wire mode has the advantage of not relying on critical timing from the Master device.

The MEDACS II further simplifies installation of either a 2-wire or 4-wire system by using a unique Bus Jumper system which eliminates both the typical RS485 and power wiring from unit to unit.

Multi-Drop and Device Addresses
The MEDACS II comes standard with one-to-one RS485 communications which allows the Master to be wired to and communicate with one Slave. With optional Multi-Drop Communications, the Master can be  connected to and communicate with up to 32 Salves. This allows the Master to identify, transmit and receive information from each specific slave.

Although each unit is equipped with an RS485 serial interface which can connect directly to a Modbus network, up to 64 channels can be connected to a gateway module. Gateways provide the physical layer and protocol conversion to common communication bus systems such as Ethernet, Profibus, Foundation Fieldbus etc.
Contact the Sales Office for details about Gateways and their current availability.

About OPC
Managed by the OPC Foundation, OPC (Object linking and embedding for Process Control) is an industry standard created with the collaboration of a number of leading worldwide automation and hardware/software suppliers working in cooperation with Microsoft. The MEDACS II is designed to meet the OPC requirements.

The goal of this standard "Plug-and-Play". By using the standard OPC client-server model, any OPC-compliant device (like the MEDACS II) will quickly, easily and seamlessly connect to another and immediately work without the need for lengthy installation procedures. The user can then concentrate more on the chosen client software package (e.g. DCDS, SCADA, HMI, Plant Scheduling) rather than the problems of system integration.

The application of the OPC standard interface makes possible interoperability between automation/control applications, field system/devices and business/office applications.

Hardware Platform
The minimum hardware requirement to run OPC are IBM compatible PC:

P100 processor or higher
64Mb Ram
200Mb free disk space
Microsoft Windows
95 (SR2) / 98 / NT4 / 2000

Thanks to the digital nature of MEDACS II transmitters, self-documentation (not feasible with earlier analog transmitters) becomes possible. In addition to the standard configuration data stored within the transmitter, are data related to the instrument itself such as Manufacturer, Part No., Serial No. ,Software Revision No., Date (which can be used to advise when re-calibration is required), Final Assembly No. and Sensor Serial No. A 32 character message facility enables additional information, such as the name of the engineer who last serviced the instrument, to be recorded within the instrument itself.

By using the appropriate software tools, a complete device history can be maintained automatically thus ensuring cost savings and reduced downtime due to better programming maintenance.


Universal Input Overview
.....Sensor .....Range
.....mA .....4-20, 20, 10
.....RTD .....Pt100, Ni120
.....T/C .....K, J, T, R, S, E, N, F, B
.....Volts .....0.1, 10, 5, 1-5
Current Input
Base Accuracy 0.05% FS 0.05% of reading
Thermal drift 300ppm/F
Input impedance 20Ω
Linearization Linear, Square root, Power 3/2, Power 5/2, Custom
Two isolated and regulated 19V power supplies are available to power the current loops, and are capable of sourcing 24mA for each channel.
RTD Inputs
Sensor Range -328 to 1,562F
Linearization BS EN 50751 / JISC 1604 / Custom
Basic accuracy 0.20.05% of reading
Thermal drift (zero) 0.006Ω /F
Thermal drift (span) 200ppm /F
Excitation current 300mA to 550mA
Lead resistance effect 0.004F/Ω
Max. lead resistance 50Ω/leg
Thermocouple Inputs  

Range (F)



to 2,498F  


to 2,192F  


to 752F  


to 3,200F  


to 3,200F  


to 1,832F  


to 1,112F  


to 2,306F  


to 3,002F  


to 9999  

0.04% FS 0.04% of reading
or 0.5F, whichever is greater


BS4937 / IEC 584-3 / Custom

Cold junction error


Cold junction tracking


Cold junction range

-4F to 158F

Thermal drift

zero  6V/F

span 300PPMF

Notes: 1. Accuracy true for 1,472F to 3,200F   2. Accuracy true for 752F to 3,002F
Voltage Inputs  


10mV, 5V, 10V, 1-5V


0.04% FS 0.04% of reading

Thermal drift


Input impedance



Linear, Square root, Power 3/2, Power 5/2, Custom

Frequency Inputs  
A wide range of input types and frequencies can be accommodated without the need for Switches or Jumpers. Totalize functions can be achieved via TFML.

Input Types

Namur, Low Voltage (>10mV), TTL, Open Collector, PFC

Frequency range

0.1Hz to 10KHz


0.003% FS

Digital Inputs  
Single channel units can also accept two external digital inputs which can be TTL, Open Collector, 24VDC Logic or Potential Free Contacts. Dig 1 is dedicated to a reset/clear function enabled by the configuration software while Dig 2 is reserved for use with TFML. Both digitals can be read via the communications and used to signal events.


Two output option types are available per channel, relay or current retransmission. The configuration of these will vary depending upon whether they are fitted on the single or dual channel transmitter.
.Current Retransmission Outputs
.Output Range
.Single Channel .0-10, 0-20, 4-20mA source or sink
.Dual Channel .4-20mA sink
.Maximum current output .<23mA
.Accuracy .0.07% or 5A, whichever is greater
.Max. power supply .30V (In SINK mode)
.Temperature stability .8A/F
Note: Max. source load 750R
Relay Outputs
Two relay options are available, either a single changeover or twin independent relays with Normally closed contacts.1
Alarm Action Off, High, Low, Deviation, Test
Hysteresis Programmable 0 to 100%
Delay Time2 Programmable
Start-up Delay Programmable
  ......AC ......DC
Max. switching voltage 48V RMS 48V
Max. current 1A @ 48V 1A @ 30V
Max. power 60VA 30W
Contact resistance <100mΩ
Electrical life @ full load 100,000 operations
Mechanical life 10,000,000 operations
  1. Contacts are Normally Closed i.e. the contact is closed at power off and when operating in an alarm condition. The contact opens in the absence of an alarm condition. The active function can be reversed in the software.
  2. Alarms must be continuously present for this period in order to be recognized.


Response Time



Programmable or Adaptive

Power Requirements

24V DC 10% @ 200 mA



Ambient operating range

-22 to 140F

Ambient storage

-58 to 185F

Ambient humidity

10 to 90% RH

EMC emissions

BS EN50081-1

EMC immunity

BS EN50082-2

Display Range

-1999 TO 9999


Each MEDACS 2000 module comes supplied with RS485 serial communications using MODBUS rtu protocol as standard:
Baud rate 19.2KB, 9.6KB or 1.2KB
Mode 2-wire or 4-wire available
Device Address Network unique address 1-255

Note: Maximum device number for Modbus is 247.


MEDACS II Instruction Manual


.......MEDACS XX / Outputs / Multi-Drop Comms
.Model & Input Code
....MEDACS 21
...   ..One Universal Input (with Display, Keys & 2 discrete inputs)
   .MEDACS 22
...   ..Two Universal Inputs
   .MEDACS 23
...   ..One Frequency Input (with Display, Keys & 2 discrete inputs)
   .MEDACS 24

...   ..Two Frequency Inputs
.Outputs Code

Output 1

Output 2

00   None None
11 (not available on MED 21 & MED 23) Current Current
13 (not available on MED 24) Current Twin N/C
22   C/O Relay C/O Relay
33   Twin N/C Twin N/C
.Modbus Multi-Drop Serial Communications Option Code
00 ..........Standard One-to-One RS485 Serial Communications
MD ..........Modbus Multi-Drop RS485 Serial Communications Upgrade
..........(Including M-Config and CD Manual)


M-Config Configuration Software on CD with Manual
M-Config Configuration Software and Manual from Web Site
M-OPC OPC Server Software


Call (800) 700-3272 for literature and pricing.  If you prefer to ask for information via the internet use the "REQUEST INFO" button at the top of this screen or e-mail = bm@statinst.com.

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