Milltronics MD-256 User manual

Instruction Manual PL-543 September 2001
MD-256 SPEED SENSOR
MD-256 SPEED SENSOR

© Siemens Milltronics Process Instruments Inc. 2001
Safety Guidelines
Warning notices must be observed to ensure personal safety as well as that of others, and to
protect the product and the connected equipment. These warning notices are accompanied
by a clarification of the level of caution to be observed.
Qualified Personnel
This device/system may only be set up and operated in conjunction with this manual.
Qualified personnel are only authorized to install and operate this equipment in accordance
with established safety practices and standards.
Warning: This product can only function properly and safely if it is correctly transported,
stored, installed, set up, operated, and maintained.
Note: Always use product in accordance with specifications.
Copyright Siemens Milltronics Process
Instruments Inc. 2001. All Rights Reserved Disclaimer of Liability
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electronic version. We encourage users to
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electronic versions as designed and authored by
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not be responsible for the contents of partial or
whole reproductions of either bound or electronic
versions.
While we have verified the contents of
this manual for agreement with the
instrumentation described, variations
remain possible. Thus we cannot
guarantee full agreement. The
contents of this manual are regularly
reviewed and corrections are included
in subsequent editions. We welcome
all suggestions for improvement.
Technical data subject to change.
MILLTRONICS®is a registered trademark of Siemens Milltronics Process Instruments Inc.
Contact SMPI Technical Publications at the following address:
Technical Publications
Siemens Milltronics Process Instruments Inc.
1954 Technology Drive, P.O. Box 4225
Peterborough, Ontario, Canada, K9J 7B1
Email: [e-mail]
For the library of SMPI instruction manuals, visit our Web site: www.milltronics.com

7ML19981FJ01 MD-256 Speed Sensor Page 1
Table of Contents
Specifications
......................................................................................2
General Operation
...............................................................................3
Circuit ..............................................................................................3
Installation
............................................................................................4
Dimensions......................................................................................4
Mounting..........................................................................................5
Mounting to a Tail Pulley .................................................................6
Mounting to a Bend or Snub Pulley .................................................7
General Installation Steps....................................................................8
Interconnection (Wiring) ......................................................................9
Terminals.........................................................................................9
Terminal Connections to Milltronics Integrators ............................10
Maintenance
.......................................................................................11
Inspection ......................................................................................11
Bearing Replacement....................................................................11
Bearing Replacement Procedure ..................................................12

Page 2 MD-256 Speed Sensor 7ML19981FJ01
Specifications
Power
•+10 to +15V dc, 30mA (from integrator)
Ambient Temperature
•-40° to 55° C (-40°F to 131°F)
Input
•Shaft rotation 0.5 to 470 rpm, bi-directional
Output
•Uni-directional open collector sinking output
•+5V dc, 25mA max (to integrator)
•256 pulses per revolution
•2 to 2000Hz
Enclosure
•General purpose
•Aluminum
Approvals
•NEMA 4x
•IP65
•CE
Cable (optional)
•3-wire shielded, 0.75mm2(18 AWG)
•Max run 305m (1000’)
Weight
•1.22 kg (2.68 lb.)

7ML19981FJ01 MD-256 Speed Sensor Page 3
General Operation
The MD-256 is a digitizing speed sensor for belt scales. It connects to the
shaft of a pulley and measures the shaft's rotation by sending pulses to the
Milltronics integrator.
This small. light-weight speed sensor features:
•High resolution for accurate measurement
•Long bearing life
Circuit
256 pulses are generated for each rotation of the MD-256 shaft. These
pulses are typically fed into a Milltronics belt scale integrator. The integrator
interprets the pulses and uses them in the calculation of belt speed, flow
rate, and material totalization.
Integrators with which the MD-256 works are:
•CompuScale
•CompuScale II
•CompuScale IIA
•CompuScale-III
•Compu-M
•Accumass BW100
•Accumass BW500
•Competitive integrators – consult your local Milltronics representative

Page 4 MD-256 Speed Sensor 7ML19981FJ01
Installation
Note: Installation must only be performed by qualified personnel.
Dimensions
Rod ∅: 8.0mm
(5/16” )
305mm
(12.0”)
89mm
(3.5”)
60mm
(2.38”)
1/2" NPT conduit entrance
(optional PG13.5 adapter available)
1/2" NPT conduit entrance
(optional PG13.5 adapter available)
Shaft ∅: 15.9mm
(5/8")
102mm
(4.00”)
159mm
(6.25”)
102mm
(4.03”)
50mm
(1.96”)
131mm
(5.16”)
111mm
(4.36”)

7ML19981FJ01 MD-256 Speed Sensor Page 5
Mounting
The input shaft on the MD-256 is coupled to the rotating shaft on a belt
driven pulley and is not externally supported. The unit’s arresting rod stops it
from rotating with the shaft and can be fitted with a spring to soften sudden
speed changes.
WARNING:
The arresting rod should only be solidly attached to the MD-256.
Fixing the rod at both ends will apply binding forces and cause the
unit’s bearings to wear prematurely.
When mounting the unit, ensure that it is concentric with the pulley shaft to
avoid stresses on the unit’s bearings.
For preferred mounting locations, refer to the associated belt scale or weigh
feeder instruction manual.
Manuals for these integrators are:
CompuScale PL-216
CompuScale II PL-261
CompuScale IIA PL-281
CompuScale-III PL-367
Compu-M PL-516
Accumass BW100 PL-531
Accumass BW500 PL-565

Page 6 MD-256 Speed Sensor 7ML19981FJ01
Mounting to a Tail Pulley
Notes:
•Distance (d) is the take up travel on the tail pulley
•When adjusting the belt take up, ensure there is play on the arrestor
rod. If the arrestor rod is pushed against the end of its travel slot,
premature bearing wear may result.
d
Angle bracket slotted
for arrestor rod
Tension Spring (supplied)
Flexible Conduit
MD-256
Angle bracket slotted
for Arrestor Rod Tension Spring
Arrestor Rod (cut to suit)
MD-256
Flexible Conduit
Belt
89mm
3.5”
≥10mm (.375”)

7ML19981FJ01 MD-256 Speed Sensor Page 7
Mounting to a Bend or Snub Pulley
Notes:
•When mounting to a bend or snub pulley only a 3/8” (10mm) drilled
hole is required for the arrestor rod.
Tension Spring (supplied)
Stringer
Belt
Flexible Conduit
MD-256
Stringer
3/8” drilled hole for
Arrestor Rod
Bend or Snub Pulley
Tension Spring
Arrestor Rod (cut to suit)
90mm
3.5”
MD-256
Flexible
Conduit
Pulley Bearing

Page 8 MD-256 Speed Sensor 7ML19981FJ01
General Installation Steps
1. Drill out pulley shaft to a depth of 64mm (2.5”) concentric to its centerline.
Warning:
Exercise caution and remain within specified tolerances.
2. Drill out and thread the set screw hole.
3. Attach angle iron bracket to work with the arrestor rod (if mounting on a tail
pulley).
4. Cut the arrestor rod to a suitable length.
5. Insert the MD-256 shaft into the pulley shaft and lock with set screw on flat
of shaft.
6. Attach spring to arresting rod and frame.
7. Encase wiring in flexible conduit to allow unit to float.
8. Wire the MD-256 to the Milltronics’ integrator. See Terminal Connections
to Milltronics Integrators on page 10 for terminal post connections.
Warning:
The arresting rod should only be solidly attached to the MD-256.
Fixing the rod at both ends will apply binding forces and wear the
unit’s bearings prematurely.
127mm
(5”) approx.
Tension Spring
Secure with
bolt or post
Angle Iron Bracket or
Conveyor Stringer Web
Example slot for
arrestor rod when
mounted to tail
pulley – use
drilled hole for
snub or bend
pulley
M8x1.25 (5/16-18 UNC)
set screw (by customer)
64mm
(2.5”)
25mm
(1”)
16.00mm (.630”) DIA.
16.07mm (.633”)

7ML19981FJ01 MD-256 Speed Sensor Page 9
Interconnection (Wiring)
Note: All wiring must be done in conjunction with approved conduit, boxes
and fittings and to procedures in accordance with all governing regulations.
Interconnection between the unit and the integrator should be made with
three-wire shielded, 18 AWG cable.
Ground the shield at the integrator end ONLY.
Note: Flexible conduit is recommended so that excess stress is not applied
to the shaft bearings.
Terminals
1 – +15V dc
The positive power supply from the integrator connection.
2 – Clockwise Speed Out
The positive output connection of the measurement loop. This output is only
used when the sensor is rotating clockwise.
3 – Counter-Clockwise Speed Out
The positive output connection of the measurement loop. This output is only
used when the sensor is rotating counter-clockwise.
4 – Common
The common connection used as a reference point with the integrator.
GND – Ground
A ground connection. Do not use this ground for the cable shield.
Note: Ground the cable shield at the integrator end only!

Page 10 MD-256 Speed Sensor 7ML19981FJ01
Terminal Connections to Milltronics Integrators
MD-256 1
+15V
2
CW
3
CCW
4
Cmn GND
CompuScale 1 2 2 4 N/C
Compu II 15 16 16 14 N/C
Compu IIA 12 13 13 14 N/C
Compu-M 11 12 12 13 N/C
Compu III 30 31 31 32 N/C
Accumass BW100 8 7 7 6 N/C
Accumass BW500 19 16 16 17 N/C
Determine the pulley shaft rotation on the end of the pulley shaft to which
the MD-256 is attached.
If the pulley shaft rotates clockwise, connect the appropriate wire to
terminal 2.
If the pulley shaft rotates counter clockwise, connect the appropriate wire
to terminal 3.
WARNING:
Do not connect terminals two and three at the same time.
Note: N/C indicates the terminal is not normally connected.

7ML19981FJ01 MD-256 Speed Sensor Page 11
Maintenance
Inspection
Periodically the cover should be removed and the enclosure and circuit
board should be cleaned for dust and grime buildup. If cleaning is required,
disconnect the power and use a vacuum cleaner and a clean, dry
paintbrush. While the cover is off, check all electrical contacts for corrosion
and evidence of arcing.
Bearing wear is detected by excess play or sound. If the bearings exhibit
excess play or produce an unreasonably loud sound, they should be
replaced.
Bearing Replacement
The unit’s bearings should be periodically checked for corrosion, wear, and
seizing. The bearings' life depends on the mounting, the severity of the
application, and the surrounding environment. Sealed bearings are used so
that lubrication is not required.
The bearing will wear prematurely if there is any force applied to the MD-256
body. Ensure that only flexible conduit is used on the unit and that it is not
exerting force on the unit.
e
Printed Circuit
Board
a
d
c
d
fMounting
Screws
a
d
c
e
d
f
Shaft

Page 12 MD-256 Speed Sensor 7ML19981FJ01
Bearing Replacement Procedure
To replace the bearings when they are worn follow these steps.
Removing the Bearings
1. Remove the MD-256 cover.
2. Remove the wiring from the terminal block.
3. Remove the unit from its installation.
4. Unscrew the circuit board fixing screws.
5. Remove the circuit board and store in a static-free bag or equivalent “safe”
area.
6. Remove the first bearing’s Cclip (part A) using retaining ring pliers.
7. Gently drift the unit’s shaft out of the housing. One bearing should come
with the shaft and one should remain in the housing.
8. Pull the bearing off the shaft.
9. Drift out the bearing and rawhide seal (part F) from the housing.
10. Clean the housing with a rag.
Replacing the Bearings
1. Warm the housing in hot water to expand the metal.
2. Remove from the water and completely dry with a clean rag.
3. Insert the rawhide seal (part F) into the housing.
4. Slide one of the new bearings (part D) into the housing. Make sure it fits
snugly against the end of the housing.
5. Slide the second bearing onto the unit’s shaft.
6. Gently drift the shaft back into place. It is in place when you can see the
groove for the Cclip (part A). Do not damage the pin on the end of the shaft
because it is required to turn the encoder.
7. Replace the Cclip (part A)
8. Replace the circuit board and ensure correct alignment of the rubber
coupling and the shaft pins.
9. Replace the mounting screws for the circuit board.
10. Reconnect to the installation.
11. Rewire the terminal block.
12. Replace the MD-256 cover.
Replacement Parts
Part numbers and suppliers for the user-serviceable parts in the MD-256 are:
Part Supplier Part Number
Boston Bearings, 1623DC
Bearings (parts D)
Nice Bearings 16232RS
C Clip (part A)TRUARC R3000-137
C Clip (parts C)TRUARC R3100-62
Rubber Connector (part E)Milltronics 21420010-00
Dust Seal (part F)Chicago Rawhide 6141

*7ml19981FJ01*