RAZORBILL MP240 User manual

USER MANUAL
Version 1.1 (released 14 April 2021)
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MP240: HIGH ISOLATION
MULTIPLEXER
The MP240 is a Double pole, quad throw fully shielded coaxial
multiplexer designed for use in high impedance measurement
systems.
This multiplexer can be used in conjunction with other Razorbill
Instruments products, it is ideal for use with devices such as the
UC200 that contain more than one capacitive sensor, or in cases
where more than one stress or strain cell is used simultaneously.
The MP240 may be controlled by USB or by a digital input. The
digital input is compatible with Andeen-Hagerling capacitance
bridges.

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MP240: HIGH ISOLATION MULTIPLEXER
SCOPE OF USE
The multiplexer is intended to be used by research scientists and
trained laboratory users, not household consumers.
Consequently, some basic understanding of the conventions
regarding the use of sensitive laboratory equipment is assumed.
This document is designed to allow the end-users to safely and
efficiently set-up and operate the MP240 High Isolation
Multiplexer and use it in conjunction with other Razorbill
Instruments products. The document is also designed to draw
attention to any risks and hazards involved in operating the
MP240 and the steps necessary to minimise them.

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MP240: HIGH ISOLATION MULTIPLEXER
TABLE OF CONTENTS
Scope of use.............................................................................2
Table of Contents.....................................................................3
CE Declaration of Conformity.................................................6
UK Declaration of Conformity................................................7
Supplier’s Declaration of Conformity (USA)..........................8
Disposing of your MP240........................................................9
Suitable Operating Environments..........................................10
Operating Modes ...................................................................10
Getting Started.......................................................................11
Reading the Front Panel ....................................................11
Back Panel Layout.............................................................13
Typical First Time Set-up..................................................14
Technical Discription ............................................................15
Grounding Notes................................................................15
USB Serial communication ...............................................17
Microsoft Windows.......................................................17
Linux, Mac OS and other systems.................................18
Using the digital input port................................................18
Pin allocations................................................................19
Enable pins ....................................................................19
Power supply pin...........................................................19
Electrical ratings............................................................20
SCPI Command Reference....................................................21
Command list.....................................................................22

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MP240: HIGH ISOLATION MULTIPLEXER
SCPI core commands.........................................................23
SYSTem commands...........................................................31
ROUTe commands.............................................................32
MODE commands .............................................................35
Example Code Snippet.......................................................37
Caring for your MP240 Multiplexer......................................38
Installing a Firmware Upgrade ..........................................38
Cleaning.............................................................................38
Firmware licencing information.............................................38
SCPI-PARSER...............................................................39
LUFA.............................................................................40

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MP240: HIGH ISOLATION MULTIPLEXER
Size
Length
180 mm
Width
185 mm
Height
65 mm
Weight
approx. 1.2kg
Power supply
USB operation
5 V, 200 mA
Digital Input Port
5V, 100 mA
Switched Signal
Max voltage
30 V
Recommended current
< 10 mA
Max switching current
400 mA
Max carrying current1
1000 mA
Switching behaviour
order
Break before make, 3 ms typ.
topology
Double pole quad throw, or as
independent relays (USB control
only)
Unconnected outputs are
grounded
Max switching speed
5 s-1
Switching cycles
> 106at maximum current
> 108at recommended current
Isolation
Typical use case2
<2 aF
Connectors
Switched signals
BNC
USB
USB-B
Digital input
D Sub 15
Ground
4mm plug, fork, or bare wire
Materials
Enclosure
Powder coated aluminium
Front and rear panels
Printed aluminium
See also: Electrical specifications of the digital input port on
page 20
1
The multiplexer must not be switched when the max switching current is
exceeded
2
When the multiplexer is used with an AH2550 capacitance bridge to
measure a capacitance of 1 pF, changing the adjacent channel from <10aF to
100nF causes a spurious change of less than (0.3+2i)aF on the 1pF
measurement.

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MP240: HIGH ISOLATION MULTIPLEXER
CE DECLARATION OF CONFORMITY
Manufacturer
Razorbill Instruments Ltd
Manufacturer’s
Address
Unit 8
Castlebrae Business centre
40 Peffer Place
Edinburgh
EH16 4BB
CE Mark
The manufacturer hereby declares that the product
Product Name
High Isolation Multiplexer
Model Number
MP240
has been tested to the following standards
EN61326-1:2013
and complies with the following European directives
2014/30/EU
EMC-Directive
Dr Alex Ward
Managing Director

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MP240: HIGH ISOLATION MULTIPLEXER
UK DECLARATION OF CONFORMITY
Manufacturer
Razorbill Instruments Ltd
Manufacturer’s
Address
Unit 8
Castlebrae Business centre
40 Peffer Place
Edinburgh
EH16 4BB
UKCA Mark
The manufacturer hereby declares that the product
Product Name
High Isolation Multiplexer
Model Number
MP240
has been tested to the following standards
BS61326-1:2013
and complies with the following UK legislation
Electromagnetic Compatibility Regulations 2016
Dr Alex Ward
Managing Director

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MP240: HIGH ISOLATION MULTIPLEXER
SUPPLIER’S DECLARATION OF
CONFORMITY (USA)
This Declaration of Conformity is hereby issued according to
Chapter 1, Subpart A, Part 2 of Title 47 of the Code of Federal
Regulations by:
Razorbill Instruments Ltd
Unit 8, Castlebrae Business centre
40 Peffer Place, Edinburgh
EH16 4BB
MP240 High Isolation Multiplexer complies with the
applicable requirements of FCC Rule Part 18
RESPONSIBLE PARTY located in the United States:
Testing Partners LLC
18200 SR 306
Chagrin Falls, OH 44023
[e-mail]
The responsible party warrants that each unit of equipment marketed
under this Declaration of Conformity will be identical to the unit tested
and found acceptable with the standards and that the records maintained
by the responsible party continue to reflect the equipment being
produced under such Supplier’s Declaration of Conformity continue to
comply within the variation that can be expected due to quantity
production and testing on a statistical basis.
(signed)
By: Dr A. Ward
Date: 21-01-21

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MP240: HIGH ISOLATION MULTIPLEXER
DISPOSING OF YOUR MP240
As an electrical good, the MP240 must not be
thrown away in normal waste disposal for
environmental and ecological reasons.
For products sold to and owned by institutions
based within the EU or UK, Razorbill
Instruments will be happy to arrange for this
product to be picked up and disposed of
properly at the end of this products life. This is
providing that the product has not been disassembled or
contaminated. This is part of Razorbills commitment to the
Waste Electrical and Electronic Equipment (WEEE) Directive of
the European Community and the corresponding national laws.
For products outside the EU or UK, please dispose of the product
using a specialised waste recovery, not in ordinary commercial or
household waste.

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MP240: HIGH ISOLATION MULTIPLEXER
SUITABLE OPERATING ENVIRONMENTS
The MP240 multiplexer must only be used under the following
operating conditions
•Indoor use only
•Ambient temperature 5°C - 40°C
•Humidity < 80 % (non-condensing)
OPERATING MODES
The MP240 has three operating modes, which are determined by
which cables are connected to the rear panel:
USB Only. The Multiplexer will start in this mode if a USB
cable is connected. The microcontroller is running and
controls both the multiplexer functionality and the front panel
LEDs. Power for the microcontroller is drawn from USB.
Power for the relays is drawn from the digital input port if
available, or from USB if not. Control signals from the digital
input port are ignored. The high and low relay banks can be
independently controlled in this mode.
Digital Input Only. The multiplexer will be in this mode if a
digital input cable is connected, but USB is not. The
multiplexer functionality is directly controlled from the input
port. The microcontroller does not run, and the front panel
LEDs do not function. This mode may slightly improve nose
levels compared to the other two. The high and low relay
banks will operate congruently in this mode.
Digital Input with USB monitoring. This mode is set by
starting the multiplexer in USB Only mode, then sending a
mode-change command by via the USB interface. In this
mode, the Digital Input Port controls the relays, while the
microcontroller monitors them, operates the LEDs and
responds to serial commands. If an attempt is made to operate

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MP240: HIGH ISOLATION MULTIPLEXER
the relays over USB, the error light will illuminate, and the
command will be ignored. The high and low relay banks will
operate congruently in this mode.
GETTING STARTED
Reading the Front Panel
Figure 1. The front panel of the MP240
As the primary mode of control of the multiplexer is using serial
commands over a USB connection, the front panel does not
feature any input controls and provides only limited information
via 6 LED indicators.
High relay bank,
switched terminals
Low relay bank,
switched terminals
High relay bank,
common terminal
Low relay bank,
common terminal
Indicator LEDs

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MP240: HIGH ISOLATION MULTIPLEXER
Indicator LEDs
Power LED. This will show a continuous green light when the
control box is drawing power from USB. It does not illuminate
when the digital input is used alone.
Error LED.This light will illuminate red to indicate that an
error has been stored. It will go out once that error has been
cleared by the PC, or when the device is reset.
Channel Indicators. When the LED illuminates, the
corresponding channel is connected to the COM terminals.
When the LED is extinguished, the corresponding channel is
connected to ground. If the High and Low relays of a given
channel are configured differently, the LED will flash.
BNC connectors
Hcom Terminal. This BNC terminal is the common connection
for the high-side relay bank. It can be connected internally to
terminals H1to H4. This terminal would typically be connected
to the output terminal of your measurement device, such as an
LCR or Capacitance Bridge. The terminal on the measurement
deice is typically labelled “high”, “force”, or “excite”
Lcom Terminal. This BNC terminal is the common connection
for the low-side relay bank. It can be connected internally to
terminals L1to L4. This terminal would typically be connected to
the input terminal of your measurement device, such as an LCR
or Capacitance Bridge. The terminal on the measurement device
is typically labelled “low”, “sense”, or “measure”
H1to H4.These BNC terminals can be connected to the Hcom by
internal relays, and are connected to ground when not connected
to Hcom.These would typically be connected to the yellow-
marked coax cable on a Razorbill instruments strain cell, or to
any other device you with to measure

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MP240: HIGH ISOLATION MULTIPLEXER
L1to L4. These BNC terminals can be connected to the Lcom by
internal relays, and are connected to ground when not connected
to Lcom.These would typically be connected to the black-marked
coax cable on a Razorbill instruments strain cell, or to any other
device you wish to measure
Back Panel Layout
Figure 2. Back panel layout
USB Port. A type B USB port. To use the Multiplexer in USB
mode, or digital input mode with USB monitoring, connect a
USB cable from the PC to this port. If you wish to use the
multiplexer in digital input mode only, leave the USB port
empty. If a USB cable is connected, the multiplexer acts as a bus-
powered USB2.0 Full Speed device.
Digital Input Port. This 15 pin D-Sub connecter can be used to
control the multiplexer directly. It is compatible with the
“switch” output on Andeen-Hagerling Capacitance bridges. If
using the Multiplexer in USB mode, this connector should be left
empty.
Digital input port
USB port
Chassis ground
terminal

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MP240: HIGH ISOLATION MULTIPLEXER
Chassis Ground Terminal. This terminal accepts a 4 mm
“banana” plug, bare wire (up to 2.5 mm2or 14 AWG), or a fork
(6 mm or ¼ in). A clean measurement ground should be
connected here. This is particularly important when the
multiplexer is used with a laptop, as the USB system may not be
connected to ground.
Compliance Information. This label displays the statutory
compliance information required for sale.
Typical First Time Set-up
•Place the MP240 on a flat clean, dry surface.
•Connect your measurement equipment to the BNC jacks
Hcom and Lcom.
•Connect the first device you wish to measure to H1 and
L1, connect the next device to H2 and L2, etc
•Connect the MP240 using the supplied USB cable
3
by
plugging into the rear panel USB port and any available
USB port on the PC.
•Install the correct drivers onto an available computer
terminal to be used as the control PC. The drivers are
available on the Razorbill Instruments website.
•The control PC should register the MP240 as a
connected device. It will appear as a virtual serial port.
•The MP240 is now ready to use. It will receive and
execute the SCPI commands defined in this document.
3
The supplied cable is good quality and includes EMI suppression ferrites.
The MP240 was tested for EMC compliance with this cable and is not
guaranteed compliant with other cables.

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MP240: HIGH ISOLATION MULTIPLEXER
Use with Andeen-Hagerling Bridges
When used with a capacitance bridge from Andeen-Hagerling,
the USB connection is not required, and noise will be lower if it
is not connected. If it is not connected, the front panel LEDs will
not illuminate.
The bridge should be configured with an average time of 7 or
higher. This triggers a “cold start”which is required if the
measured capacitance changes a lot of if the parasitic capacitance
of the cables changes. In future firmware versions, it is possible
that using the sample switch output will trigger a cold start, in
which case this will no longer be necessary. Contact Andeen-
Hagerling for further details.
TECHNICAL DISCRIPTION
The multiplexer contains two identical relay banks, these are
intended simultaneously switch the high and low measurement
arms of a capacitance bridge, LCR or similar measurement
instrument. Each of these relay banks consists of four BNC
connectors that can be either grounded or connected to the COM
terminal in the corresponding bank. The layout is illustrated in
Figure 3.
Grounding Notes
The analogue grounds for the High and Low relay banks are
internally connected to the case. This arrangement improves
electromagnetic emissions and ensures ground is provided to all
cable shields irrespective of other attached equipment. When
other attached devices also ground the cable shields, there is a
possibility of ground loop noise being introduced. Testing with
an Andeen Hagerling 2550A in a typical lab environment did not
show any reduction in performance with this arrangement, but
the analogue grounds have the potential to be isolated from each
other and from the case ground should this be necessary. To
isolate the analogue grounds, open the upper case and remove the

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MP240: HIGH ISOLATION MULTIPLEXER
jumper wires from the relay boards to the case
4
. When the
jumpers are removed, analogue ground is derived from the shield
of the connected cables in each bank.
Figure 3 - block diagram
The case ground is connected to the USB ground and digital
input port ground. It is recommended to attach the case ground to
a clean ground. This is particularly important if the multiplexer is
4
The device was tested for FCC, CE and UKCA compliance with the
jumpers in place. It is not guaranteed to be compliant without them.

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MP240: HIGH ISOLATION MULTIPLEXER
connected to a laptop or similar portable computer, as these may
not provide a ground connection through the USB cable.
USB Serial communication
The MP240 multiplexer uses a USB virtual serial port to
communicate with a computer. The multiplexer acts as a bus-
powered USB2.0 full speed device, and requires up to 200 mA
from the computer or USB hub to which it is connected. Any
modern PC or powered USB hub will supply this level, but use
of unpowered hubs could lead to interruptions, depending on
what other devices are attached. You can also use standards-
compliant USB extenders. The standard allows for one “dumb”
5 m cable, and up to five “active” extenders or hubs, each adding
5 m of cable.
Microsoft Windows
Razorbill instruments supports the MP240 on Microsoft
Windows 7 and higher.
Before using your multiplexer, you should install the necessary
drivers for your operating system; these are available on the
Razorbill Instruments website. The Multiplexer may work with
windows built-in drivers, but our drivers have several advantages
including improved reliability of the USB link, and the correct
device name appearing in system menus.
When our drivers are installed and the multiplexer is plugged in,
a new serial port will appear on your system. Your operating
system will normally allow you to set baud rate, stop bits, parity
etc. for this port, but as there is no physical serial connection
within the multiplexer, these settings have no effect and should
be left at the defaults.
Once the virtual serial port has been created, it can be accessed
directly as a serial port, or indirectly using, e.g. VISA.
Whichever way it is used, you will also need either a terminal

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MP240: HIGH ISOLATION MULTIPLEXER
emulator to type commands and receive responses, or a program
or script to integrate the supply with your measurement system.
A basic example using python is included on page 37.
Alternatively, Razorbill Instruments may be able to provide a
software tool with a graphical user interface.
Linux, Mac OS and other systems
The MP240 implements USB CDC and is likely to work on most
modern platforms. We are not able to offer assistance with
communications issues on operating systems other than
Microsoft Windows.
Using the digital input port
The Digital input port is designed to be compatible with the
sample switch output of Andeen Hagerling capacitance bridges.
It can also be used to control the multiplexer from any logic
source between 3 V and 25 V.
If power is provided to the multiplexer through the digital input
port, this will be used to drive the relays in preference to power
derived from USB. This could reduce electrical noise,
particularly if the USB system in the computer has deteriorated.
The connector is a standard 15 pin D-Subminiature male socket
(with male pins and female screw locks). This is distinct from
high density (HD) D-Sub connectors, which have three rows of
pins.
Figure 4 - Digital input port pin numbering, view onto mating face
of rear panel connector

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MP240: HIGH ISOLATION MULTIPLEXER
Pin allocations
The pins are numbered according to Figure 4 and the pin
numbers are also moulded into the connector. The pin allocations
are shown below:
Pin
Function
1
Channel 1 Enable
2
Channel 3 Enable
3
NC
4
NC
5
Ground
6
Power (+5 V)
7
NC
8
NC
9
Channel 2 Enable
10
Channel 4 Enable
11
NC
12
NC
13
NC
14
NC
15
NC
Shell
Ground
Enable pins
The enable pins are active high. When a channel enable pin is
driven high, the relevant relays in both the high and low bank
will be set to connect the corresponding BNC connector to the
COM BNC connector. When a channel enable pin is pulled low
or left floating, the corresponding BNC connectors will be
connected to ground.
Power supply pin
Pin 6 is intended for use with Andeen Hagerling capacitance
bridges, which have a well-regulated 5V output. The power input
is only minimally protected and can be damaged by e.g. reverse
connection or overvoltage. There is a PTC fuse, if the fuse

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MP240: HIGH ISOLATION MULTIPLEXER
operates, disconnect the power supply or capacitance bridge. The
fuse will automatically reset within a few minutes.
Power supplied to pin 6 from a source other than an Andeen
Hagerling capacitance bridge must be well-regulated and should
have the minimum practicable noise or ripple. Power supplied in
this way will be used to operate the relays. Internal filtering and
additional voltage regulation are provided, but there remains
some potential for excessive noise on this pin to affect the signal
path.
Warning! A voltage between 0.2 V and 3.8 V
applied to pin 6 when USB power is also
connected may damage the multiplexer.
Confirm the voltage of the power supply is
correct and has sufficient current available to prevent voltage
sag.
Electrical ratings
Channel
Enable Pins
Absolute maximum voltage
25 V
Absolute minimum voltage
-25 V
High state voltage
> 2.6 V
Low state voltage
< 0.75 V
Pull-down
5 kΩto ground nominal
Power supply
Pin
Absolute maximum voltage
5.5 V
Minimum functional voltage
4 V
Recommended voltage
5 V
Max current draw
100 mA nom.
(140 mA fuse)