Archive for Application Notes

Wireless Control of Life Support System in an Exotic Aquarium for Show Animals

Wireless Control of Life Support System in an Exotic Aquarium for Show Animals


Park engineers have an application sending a 4/20mA signal from an ORP (Oxidation Reduction Potential) sensor to a Control Room approximately 500 feet away.

The ORP sensor is used to electronically monitor the amounts of sanitizer and other chemicals in the water, before it enters the large holding tank.

Rain or shine, a ladder is climbed to the top of a pump house building several times everyday to take readings. This posed a safety and health risk to the operator as well as only provided sporadic measurement cycles.

The EPA requires monitoring of this chemical system for both human and animal safety.

More Info: Frequency Hopping Spread Spectrum Technology

More Info: Value of Isolated Signal Conditioners


The ORP monitor where the reading was taken is in a hard to reach location at the top of a pump house on the side of the tank.

Due to a large amount of sidewalks and other obstacles, it was not cost effective to run wires from the sensors to the Control Room.


Checking the 500 foot line of sight between the Transmitter and Receiver locations indicated there was a 50 foot elevation difference. The check of the antenna path also indicated there was a large building near the Receiver. There are also several trees in the antenna path.

More Info: How to calculate your antenna needs


DR9011 With 3 Element Yagi Antenna

DR9011 With 3 Element Yagi Antenna

Use a 900 MHz Band Transmitter (DR9011, 2 analog and 4 switch inputs) at the top of the building to monitor the 4/20mA signal from the ORP sensor.

The DR9011 was installed inside a NEMA 4X housing. A small 3” high 2.1dBi gain vertical antenna was mounted on the top of the NEMA 4X housing.

Use a 900 MHz Band Receiver (DR9021, 2 analog and 4 switch outputs) at the LSS Control to receive the data coming from the DR9011 Transmitter.

This unit was installed inside a pre-existing control panel. Along with a wall mount 3 element directional Yagi antenna (8dBi gain) to the top of the LSS (Life Support System) Control building.

The use of the Omni directional antenna at the sensor end allowed the signal to be transmitted across a wider path. In using the Yagi antenna at the receiver side, the install crew was able to choose the best location and path for pointing the Yagi antenna.

The trees and building posed difficulty by either blocking part of or potentially causing a reflected signal in the Fersnel Zone. The Yagi helped eliminate this due to its narrow beam width.

This system has been reliably sending data since June 2007.

Variable Speed DC Drive Application To Reduce Noisy Control Signals


Oil Exploration Rig Application


Mighty Module Wilkerson Instrument

Mighty Module

Specifications                   I/O Manual


A flat bed trailer was outfitted with a 150 KW generator, two variable speed DC motor drives, and the necessary mechanical equipment to allow computer control of the system as an oil exploration rig.

One motor drove the drill, the other drove the hoist. The variable speed drives were SCR inverters with rectifiers to provide a variable DC voltage to each motor. The system had electronic torque limiters.

The drilling operation was computer controlled and two computers output a total of 2 analog signals (motor speed) from digital to analog converters and monitored 4 analog signals from tachometers and torque limiters. Six of Wilkerson Instrument’s MM4380A Isolated DC Transmitters were used in the analog paths to provide isolation and prevent ground loops. The customer built these Rigs and leased them for oil exploration. The customer called for help when the system did not work properly.

All six analog signals had noise, from the SCR drives, imposed on the outputs of the MM4380A signal conditioners. The noise amplitude was as high as the full scale DC process signal.

A discussion with the customer revealed they always had severe noise problems with the rigs and the best they ever accomplished was to get the noise down to about 20% of the full scale DC signal. The rigs seemed to work satisfactorily with this noise level so they lived with it.

This rig was the first to be built where they had attempted to deal with the noise. The user of the rigs usually parked the rig on a dirt mound about 8 to 10 feet above the surrounding terrain. They drove a ground rod into the earth at the bottom of the mound and used this as the system ground for the rig.

The customer faxed Wilkerson Instrument Co. drawings of the wiring of the analog part of the controlled system. It was discovered that all analog signals were run in shielded pairs. The shields were connected to circuit common on the computer as well as the MM4380A. All of the shields were also connected to a common point on the electrical box that held all of the equipment. This box was connected to the system ground.

The customer agreed with our suggestion and rewired the shielded cables so the shield of each cable was connected only to the circuit common of the driven device. They were also disconnected from the common ground point (and each other). This simple change dropped the SCR noise to less than 1% of the full scale DC signal and the customer was delighted.

The cause of the noise can be read at:  WIRING FOR TROUBLE FREE SIGNAL CONDITIONING  PDF


Solutions provider for signal conditioning and process control instrumentation – Wilkerson Instrument Company Inc – Copyright 2012



Get every new post on this blog delivered to your Inbox.

Join other followers: