Tension Calibration for a Winch Monitoring System

In a previous posting we discussed the technique of calibrating the payout line parameter for winch applications.

It is also important to understand the technical challenges of calibrating the tension line parameter of your winch monitoring system.

The calibration of a tension measurement system can be achieved through several methods.

MTNW employees calibrate two Foss tugs in Puget Sound by having them pull against each other

It’s always best to conduct a live calibration of the winch monitoring system once the sensors, displays and line have been installed and the wrap angles determined and identified to be fixed (more on the wrap angle in another blog).

Since tension sensors behave in a very linear fashion, meaning that their electrical output has a linear relationship with the load applied to the sensor itself, a single, two-point calibration (a low tension and high tension reading) is often sufficient to calibrate a tension monitoring system.

We typically can calibrate a system to better than ±0.5% without too much trouble.

Calibrating a winch monitoring system requires the use of an additional (previously) calibrated tension sensor, typically a tension link. Make sure that the tension link has a valid certificate, that it is not expired. You can often rent these for days or weeks at a time.

Calibrations are typically good for a year for these types of devices.

Winch tension calibration often requires additional support from your marine operations group because they will need to provide the winch operator, a previously calibrated tension sensor, deck hands to rig the tension link to the winch line and winch time to complete the calibration procedure.

There have been many times we have been scurrying around the deck to get this done before the vessel leaves the port or the fuel truck shows up (all deck work ceases when the vessel is fueling).

One side of the tension link should be secured to the winch line and the other should be secured to either a rigid solid structure like the deck or weights of known values.
The winch operator can now carefully haul in the line slowly till the desired tension is reached or the weights have been lifted off the ground.

We prefer to use weights as they provide a more stable measurement platform. Because the winch line is basically a big spring, if you are securing your winch line to the deck the system can relax causing the tension link reading to change before the data is applied to the display.

Our method is to collect the tension sensor analog output (mA, volts, mV, etc) at two known line tensions, one high and one low. The low value can be either zero or near zero, depending on the application. The high point can be either the breaking strength of the line or the maximum tension the deployment can expect. It should be noted that the breaking strength of the line is a much higher value than the working tension range of the winch operations. Setting the high calibration point to the breaking strength will reduce the accuracy of the system at lower tension ranges.

We hardly ever calibrate to the maximum breaking strength of the wire rope as the forces required make the rigging difficult and increases the likely hood of something breaking and creating a safety hazard.

Always remember to stand way from the direction of the winch.

I was fortunate once to be able to walk away from an installation in Chile were I was not positioned properly and a snatch block gave way shooting across the deck and denting the bulkhead between myself and the Chief Engineer.

In terms of calibration, note the sensor output at the low and the high points and enter the data into your display. The LCI-90i display will automatically calculate the slope and offset of sensor output verses applied load and apply this over the complete working range of the sensor.

The LCI-90i makes calibration easier than most other systems because the input fields and buttons are right on the main face of the display. Inputs can be changed and updated on the fly without the use of an additional computer. Analog sensor values are displayed during the calibration making the calibration quick and easy.

If higher levels of accuracy are required, you can input more calibration points to develop a “look up table”. This can also be used if the sensor is exhibiting non linear characteristics. Synthetic ropes often will deform under tension and will perform non-linearly. The LCI-90i display allows the end user to develop and reference a “look-up” table without additional programming or a PLC interface.

Other calibration techniques can be used such as shunt calibration, voltage substitution, etc. These techniques, however, are hardly ever used and not worth learning about.

Good luck in your calibration. If you have questions, please don’t hesitate to give us a call.

Tags: barge mooring, cable tension, cable tension monitoring, Line Tension, mooring line tensiometer, Puget Sound, tugboat

This entry was posted on Wednesday, April 7th, 2010 at 6:38 pm and is filed under Line Control Systems. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.

US Coast Guard Uses an MTNW Running Line Tensiometer for R&D

Through one of our partners, Dillon Quality Plus, the Coast Guard purchased and used our HRT-3mm Running Line Tensiometer (or line rider) to measure the cable tension loads during some qualification testing on an improved rescue hoist for the Coast Guard H-65 Dolphin Helicopter.

An HH-65C flight crew hoists an injured hiker to safety from a mountain peak in WA at an altitude of 6,300 feet.

The hoist was improved by adding a clutch designed to release if the cable forces exceed a known value.  The Coast Guard tested the release force pulling on the cable at various speeds from 1 in/s to 30 in/s.  After the hoist passed this testing, the Coast Guard then conducted a number of drop tests that consisted of a 600 pound mass attached to the end of the cable and various amounts of slack in the cable from 1 to 5ft.

During all testing, the tensiometer (or dynamometer) was attached to the cable and the load output was recorded.  The HRT-3mm system worked perfectly.

The HRT-3mm is designed to measure running line cable tension loads from 0-13,000 lbs.  It only weighs 30lbs and is compact but reliable.

Tags: cable tension monitoring, calibration, Coast Guard, HH-65C, HH-65C Dolphin Helicopter, Injured Hiker, Line Rider, Line Tension, Running Line Tensiometer, Search and Rescue, tensiometers, tension meter, winch payout, winch tension

This entry was posted on Wednesday, February 17th, 2010 at 3:34 pm and is filed under Line Control Systems. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.

Cable Tension Meters (or is it Tensiometers or Dynamometers?) for Barges, Rigs, Construction, and Pipeline Inspection.

We often get asked questions about the difference between tension meters, tensiometers, and dynamometers. There is good reason for the confusion because many different industries use the same words for different applications. For example, the word tensiometer, which we use to describe our primary cable tension/payout monitoring equipment, is also used to describe a soil moisture monitor, and dynamometer is a word that was widely used within North America for a device for measuring automotive horsepower.

At Measurement Technology NW we focus on measuring cable tension in many different applications (from 1,000 lbs-1,000,000 lbs) and we use the words tensiometer (dynamometer) and tension meter interchangeably. Even though the words mean much the same thing, our tensiometers can be provided with an extra sensor to measure payout and speed – two line control parameters that are not always considered when referencing a standard “tension meter”.

Tensiometers can be of two main styles; running line tensiometers (RLT’s) are designed to ride the line and provide measurements of tension, speed and/or payout as the line moves through the unit. Static tensiometers are devices that clamp onto to non-moving lines and only need to provide a measurement of line tension.

Our customers use MTNW tension monitoring devices in applications such as: offshore mooring, barge mooring, oceanographic payload monitoring, ROV launch and recovery system monitoring, tethered pipeline inspection (or pigging) monitoring, etc. Usually it is a safety requirement that drives the procurement of these tensiometers.

Here is a picture of a barge mooring monitoring project for which Ombak Marine Group in Kuala Lumpur has installed a group of MTNW’s tensiometers. These units are defined as tensiometers (or dynamometers) because we are helping them measure all three line parameters.

Our running line tensiometers are 3 sheave devices that detect tension by the deflection of the strain gauge transducer installed in the load pin that is in the center of the top sheave.

Here is another picture from an NPCC barge mooring monitoring project. NPCC, based in Dubai, ordered 8 running line tensiometers (or dynamometers) from us. You can see how we have installed this device in a compact area under a platform. It is tethered from above to avoid damage in a slack line event and tethered fore and aft to prevent rocking.

Whether you call it a tensiometer, a tension meter, or a dynamometer (and hopefully we’ve cleared away some of the confusion), we build the most rugged, accurate, and easily installed cable tension monitoring device in the industry.

Tags: cable tension, cable tension monitoring, tensiometers, tension measurement, tension meter

This entry was posted on Tuesday, January 12th, 2010 at 9:37 pm and is filed under Line Control Systems. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.

Dillon Tensiometer (Dynamometer) Upgrade for NDT Pipeline Pigging & Inspection Services

We recently completed a refurbishment and upgrade to an older Dillon Tensiometer model owned by NDT Services. Frank Vignall, from NDT, has been using a 40KIP Dillion Tensiometer for many years to support his pipeline inspection services. In his work he mounts the tensiometer on a cable used to pull a package through a test pipeline to determine how much pressure it will require to push a similarly-sized scientific package through a fluid or gas pipeline for customers. NDT Services sends their scientific packages through pipes to find defects and identify pipe locations where repairs need to be made. Their old Dillon tensiometer had parts that were worn out and no longer serviceable. You can see in the pictures below that in our upgrade we installed modern wiring, a strain gauge module and a Hall Effect sensor to measure cable payout.

The load cell on the Dillon unit was still functional but the rotational sensor had failed. MTNW designed a special gear tooth sensor and mounted it to the spur gear on one of the outer sheaves. In this manner we were able to obtain a digital quadrature pulse train that MTNW’s LCI-90 processed into a real-time display of speed, payout and cable direction. In the course of this retrofit MTNW worked with engineers from Dillon, the spur gear manufacturers, and our rotational sensor manufacturer. In the end we were able to measure 72 pulses per sheave rotation with a highly accurate payout resolution. The existing load cell was found to be functional and when connected to our LCI-90 display found to be very accurate in calibration. We also installed new bulkhead connectors on both the tensiometer and display units.

This Dillon Tensiometer is over 10 years old and came from the original Dillon series. It weighs about 350 lbs. As you can see in the picture below, we now make comparable tensiometers (dynamometers) which weigh less than 1/3 of the original Dillon model but which can support a similar tension range. Our RL-60 frame size (shown below) can accommodate a tension range from 0-60KIPS. For greater accuracy, we have used custom load pins in this frame size for lower (0-20 & 0-40 KIPS) maximum loads.

We also paired this older Dillon unit with our WinchDAC software for PC logging and remote viewing of operational data. Now NDT can build and send data directly out of WinchDAC into Excel for further report building. See our WinchDAC Software for Single Winch images below.

Given that Dillon was one of the first tensiometer manufacturers in North America it has been gratifying to see how well suited our modern technology was to the functional upgrade of this older system.

Tags: cable tension, cable tension monitoring, Line Tension, winch tension

This entry was posted on Friday, January 8th, 2010 at 6:32 pm and is filed under Line Control Systems. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.

Post Update – Natural Gas Pipe Pigging & Slip Lining Application – Cable Tension Monitoring

We just spoke with Michael Kasten, President of Coordinated Wire Rope, and during the conversation he mentioned that last Friday the CD Lyon team was working with the LCI-90 and HRT-3MM tensiometer/dynamometer system (described in our last blog post) when they hit “a snag”…literally. The CD Lyon team was pigging the pipe, which means that they were dragging a device through the existing pipe looking for obstacles, when tension readings on their LCI-90 display suddenly jumped from 3,000 lbs to 13,000 lbs.

Because the LCI-90 payout measurement is so accurate, the construction team was able to go directly to the location of the stuck pig, dig down to the pipe, remove the obstacle, repair the pipe and keep pigging…all within a couple of days. This is exactly what Measurement Technology cable tension monitoring systems are designed to do! Provide fast, accurate information that prevents problems and saves you time and money.

In the picture below you can see the “pig” device that the CD Lyon team is pulling through the pipe to look for obstacles.

Tags: cable tension, cable tension monitoring, Line Tension, mooring line tensiometer, winch payout, winch tension

This entry was posted on Friday, December 4th, 2009 at 7:00 pm and is filed under Line Control Systems. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.

Natural Gas Pipe Pigging & Slip Lining Application – Cable Tension Monitoring

Based in Ventura, CA, Coordinated Wire Rope (http://www.coordinatedcompanies.com) approached us for a project that required highly accurate measurement of line tension and payout on an underground cable pulling application for their customer, CD Lyon. CD Lyon had been tasked with pigging (looking for obstacles) and slip-lining (inserting a new pipe into an old pipe) an old 8 mile natural gas pipe, and they were looking for solutions that would make the project run smoothly and efficiently.

CD Lyon planned to use a 5/8” wire rope to pull the pipe pig and new pipe slipline. They needed to measure up to 14,000lbs of tension, which is load at which the pipe lining may be damaged.

This wire rope size and tension range was a perfect fit for our compact HRT-3MM tensiometer (dynamometer). We paired this tensiometer with our LCI-90 display, which was housed in a portable and rugged Pelican case.

In the photo below you can see that Coordinated Wire Rope and NTT Fabrication built a custom winch skid, on which they mounted the Pelican case and LCI-90 display. You can see the LCI-90 and case immediately to the left of the controls for the winch.

The photo below shows how the HRT-3MM tensiometer rides the cable it is monitoring. NTT Fabrication built an articulated arm which allows for lateral movement of the tensiometer (tracking line as the winch spools) and also supports the device in the case of a slack line situation.

MTNW’s solution provided an inexpensive and portable line monitoring system without the need for winch modifications. We pre-calibrated the system before it was sent it out, and Coordinated Wire Rope found that their new LCI-90 + HRT-3MM cable monitoring system was not only easy and intuitive to work with, it worked from the moment they pulled it out of the box.

Tags: cable tension, cable tension monitoring, HRT-3MM, Line Tension, mooring line tensiometer, NTT Fabrication

This entry was posted on Friday, November 27th, 2009 at 7:24 pm and is filed under Line Control Systems. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.