Digital Panel Meters FAQ
What are the basic uses and benefits of a panel meter?
A panel meter is used to display relevant information about the system being monitored. Having the right digital panel meter can provide an effective tool for sensing and viewing critical process and tank levels.
The desired digital panel meter should be field programmable to display as percent, inches, gallons or other customizable values. In addition, the viewable LED panel meter display should be easy to read from a distance.
How do I select the best panel meter for my application?
- Determine what you want the panel meter to display for you.
- Know your input power requirements.
- Know what signal you are trying to display on the meter and if you require output voltage from the meter or relay contacts to aid in your application.
- Click here to view additional information on choosing the right panel meter along with complete information on panel meter selections available from Madison Co.
Liquid Level, Pressure Sensors and Temperature Control Frequently Asked Questions
Click a question to display the response.
1. How can I connect my float level switch to a pump or valve while protecting it from the high current that these devices use?
In most applications, a relay is required to isolate the float switch from the device. The float switch will be connected in series with a relay input coil that typically draws less than 500 mA. When the switch is closed, the relay coil is activated and closes the output contacts. These contacts turn on or off the high current required by the device.
2. How can I control my pump or valve to maintain a range of liquid in my application?
Madison can provide solutions to control the liquid level between a high and a low point. By combining a controller with two float level switch points, a pump or valve can be switched on/off automatically. This can be done using two single point float switches, or a custom multi-level float switch with the levels set an appropriate distance apart in the tank.
This may also be achieved by using a Double Pole Double Throw (DPDT) relay when combined with two level switches as shown below for "pump-up" or "pump-down" applications.
For Pump-Up Applications: For Pump-Down Applications:
Madison stocks an R2-120 Vac pump controller that can be used with float switches or conductivity probes. Madison also stocks relays and controllers to activate pumps, solenoid valves, motors and alarms. Our fluid control engineers are on-hand to assist you with these applications.
3. How can I tell if my float switch is set for Normally Open (NO) or Normally Closed (NC) operation? How can I change it from NO to NC (or vice versa)?
To begin, the "Normal" position refers to a float switch in an empty tank, or before liquid has affected the float. Each style switch is equipped with a means to identify which type of operation to which the float switch is set.
Vertical: NO/NC operation is indicated by the position of the float's witness mark (stainless steel models) or magnets (plastic models). NO is indicated by circle up (stainless steel) or magnets down plastic); NC is indicated by circle down (stainless steel) or magnets up (plastic).
Horizontal: NO/NC operation is indicated by the direction of the arrow on the hex. NO is indicated by arrow up; NC is indicated by arrow down. An ohmmeter or continuity meter can be used to verify the switch setting and operation. For vertical switches, simply connect the meter to the leads and, with the float hanging down away from the fitting, measure the switch. If the meter reads a short, then the switch is normally closed and will open on rise.
Most stock Madison float switches are shipped in the Normally Closed (NC) position, unless otherwise specified. To change the contact operation for vertical switches, remove the retaining clip and float, and reverse the float on the stem. The only exception to this is the subminiature switch (M3326/M3326-NO), for which operation must be specified when ordered, since the float is not reversible on this model. For Horizontal switches, simply rotate them 180° in their tank installation.
4. Is there a way to sense between two liquids?
Madison can furnish an Interface Float that, given two mediums, is designed to sink in one medium and float in the other. A typical application would be one where oil and water accumulate in one tank, and sensing of only a fall in water level is required (oil level is not an issue). Since a standard float of any material will float in any liquid with a specific gravity higher than the specific gravity of the float, Madison would "weight" the float to a specific gravity of 0.95. Since the specific gravity of the oil is 0.8-0.9 and that of the water is 1.0, the float will sink in the oil and float in the water. Both full-size Buna-N and polypropylene floats can be modified in this manner.
5. How do I make sure the switch I choose has the correct specific gravity?
One of the main considerations when choosing a switch is the specific gravity of the float. To make sure the float will function properly in the application, the specific gravity of the fluid must be greater than the float's specific gravity at the maximum temperature range of the application. For reference, below are specific gravities of some of our floats.
Full-Size Floats: Miniature Floats: Side-Mounted Floats:
Stainless steel — 0.55 SG, & 0.70 SG Stainless steel — 0.70 SG M5900 — 0.60 SG
Polypropylene — 0.75 SG Polypropylene — 0.80 SG Polypropylene — 0.60 SG
Buna-N — 0.45 SG Buna-N — 0.45 SG PBT — 0.75 SG
Kynar — 0.75 SG Kynar — 0.85 SG Kynar — 0.75 SG
6. Which switch material is best suited for my liquid level application?
316 Stainless Steel: For high-temperature (to 250°C), high-pressure (to 300 PSIG) and corrosive conditions. Commonly used in food processing, medical, heating and cooling equipment.
Polypropylene & Polysulfone: For acidic conditions, such as found in electroplating and metal cleaning. Another choice for lower-temperature (to 105°C) food processing applications (Madison Company uses only polypropylene that is FDA-approved for food contact). Also a good choice for general-purpose applications in commercial or consumer appliances and equipment.
Brass & Buna-N, PBT & Buna-N: The selection for petroleum-based liquids, such as lubricating oils, gasoline and diesel fuels. Widely used in storage tanks of vehicles, generators, transmissions and hydraulic systems. Other uses are in lubrication, recovery, refining and fuel processing equipment. PBT is not suitable for use at temperatures above 130°C.
Kynar: Chemical- and solvent-resistant properties make this material a problem solver for many applications. Its high-purity nature is ideal for food handling and sensitive laboratory or test equipment.
7. How can I ensure that my switch's performance will not be affected by turbulence?
Turbulence, which can be caused by a vibrating tank, intensive mixer agitation or surging of liquid during tank filling, can result in premature failure of both the switch and the relay, due to chattering. A very low-cost, reliable solution to this problem is the use of a slosh shield. This device is equipped with fluid and vent holes and surrounds the switch float to prevent erratic switch operation.
Madison stocks a complete selection of slosh shields for vertical and horizontal switches in stainless steel, polypropylene, PBT, brass or Kynar.
8. Can I customize a standard switch?
Madison Company offers a full range of value-added options, including terminations and connectors; extra-long or -short lead lengths; special cable or wire; shrink tubing for wire protection; and special sealing materials, such as Viton or Buna-N gaskets and O-rings. We can also meet special requirements with our temperature sensors, slosh shields and weather-proof or explosion-proof junction boxes.
9. Which Madison switches are explosion-proof?
Our vertical M5600 series and our horizontal M5900 series are rated explosion-proof by UL and CSA for use in Hazardous Locations, Class I, Groups A, B, C, D; Class II, Groups E, F, G; Class I. These switches are also approved by DEMKO for use in potentially explosive atmospheres EEx d IIC T2 and carry the Ex mark.
10. Are liquid level switches affected by semi-solid particles or magnetic particles in the liquid?
Yes, standard float switches may be affected by these conditions because such particles can cause a float to stick or to not operate at all. Instead, we recommend using a conductivity switch, such as our multi-point model M3784 or single level model M3850. Because our conductivity switches have no moving parts, operation of these switches is not interrupted. Furthermore, the M3827 side-mounted switch is engineered such that the magnetically actuated reed switch will not come in contact with the fluid being monitored. The float is attached to an extended pivot arm that, when moved, triggers the switch function. This switch is ideal for use in heavy-bodied liquids or in fluids containing metal particles that would otherwise be attracted to a conventional style float.
11. What industry ratings do Madison's switches have?
We have a continuing program to upgrade our list of UL and CSA approvals. Madison Company's liquid level switches have general-purpose approval as recognized components granted by UL under file number E54633 and CSA file number LR56150.
Some Madison switches are also NSF-certified for food applications.
12. Can I order a Madison switch with more than one level?
Yes, Madison offers multi-point switches in many configurations. Our full-size multi-point switches can be set for up to six levels, and our miniature switches can be set for up to four levels. They can be mounted within any vessel, utilizing male pipe threads, pipe plugs, flanges or bulkhead fittings. The length of each switch, as well as the location of the floats, can be established by the designer. For those users who want to design and install their own systems, multi-point switch kits are available in three different materials.
13. Will the 4- 20 mA or 1-5 VDC work with a PLC that is sink or source?
Yes, as long as the proper wiring is in place as shown below:
Click a question to display the response.
Slider 1. What are the advantages of Ultrasonic and Radar sensors?
When compared to other level sensors, ultrasonic or radar level sensors do not contact the material and are not affected by the color, shape or composite of the material being measure. These sensors....
- have varying distance ranges that are feild programmable and can detect many types of materials
- are not affected by dust, dirt or wet environments or by most materials, colors and surfaces
- are impervious to most materials, colors and surfaces
- are resistant to external vibration, ambient noise and infrared or EMI radiation
- provide 4-20mA output and are available with optional RS232, 485 or Hart communication
Features of Ultrasonic sensors;
- Smaller size and lower cost, ideal for smaller tanks, wells or vessels
- Detects liquids or solids in air based container from 4in. to 33ft. depending on models used
- Lend themselves easily to waters, oils, chemicals or foods in industrial to pharmaceutical applications
Features of Radar sensors;
- Ideal for large tanks or applications up to 340ft for specific models
- Accepts 24vDC or 120vAC input power for process tanks and industrial applications
- Automatically adjust power for environmental conditions or materials
- Available for explosion proof, sanitary and flood monitoring, including open channel flow applications
- Detects chemicals, oils, gases or waters with vapors, foams or solids, including Oil/Water interface
For more complete information Click Here
Slider 2. How do the ultrasonic and radar sensors work with the software?
Madison's standard ultrasonic and radar sensor models can be selected with a communication option. This option is a choice of an RS-232 or an RS-485 connection. The RS-232 is for a one sensor to one PC link, and the RS-485 is for up to multiple sensors (up to 128) to one PC. Madison supplies user-friendly software for sensors purchased with this option. Once the software is loaded onto the user's PC, the user can tailor several characteristics of the sensor so that the graphs and displays of the sensor's signals can be representative of the measurements being taken in the vessel.
Slider 3. How do I mount the sensor to assure proper performance?
Although there are several different options that can be offered, the most common is where the sensor is screwed into a standard fitting that is attached to the outside of the vessel. The sensor's face or lens is inside and just below the vessel's inside surface. The sensor should be relatively upright, aiming at the lowest part of the vessel and away from any filling source, piping, ladders, propellers, etc. that could be within the beam spread and cause a false echo. See diagrams on our mounting and applications reference pages.
Slider 4. What about dust and foam on the material surface?
Whether or not the ultrasonic echo will be interfered with depends on how dense and how reflective the dust or foam is. Once we understand what the material is and the depth of the dust/foam above the target material, the sensor selection can be made so that the signal strength can be greater, to penetrate the interference and provide reliable level measurement. If the application cannot be solved with the ultrasonic sensor, the radar sensor will most likely do the job.
Slider 5. Can the transducer housing on the end of the ultrasonic sensor be used in food applications or applications that are not suitable for the standard PVC housing?
Yes, the transducer housing is offered in a sanitary design on several standard models; refer to the catalog listing for the standard models. The transducer housing can also be designed in Teflon®, Kynar and other materials.
Slider 6. What are the thread options on the sensors?
The catalog chart lists the thread for each Madison standard sensor model. The standard thread configuration is 1" NPT. Madison can also quote the price of sensors with BSP threads, for customers who require them.
Slider 7. What are the sensor housings made of?
The Madison ultrasonic sensors' housings are PVC in dark gray. The PVC can be quoted in white and light gray as well. The Madison radar sensors' housings are aluminum, and it can also be quoted in 316 Stainless Steel. The radar antenna is white polypropylene and can be quoted in Teflon®.
Slider 8. Is the Madison radar antenna only available in the cone shape?
No, although the cone shape is preferred in applications that require sanitary surfaces or have media that tend to build up. A horn shape is also available for a higher power and better signal shape.
Slider 9. My gateway PC software doesn't communicate with my radar or ultrasonic sensor, or the communication has long delays?
The default serial port settings for the transmit and receive buffers are likely set too high in Windows 2000, NP or XP. To correct this, go to the Control Panel; select System; select Hardware; select Device Manager; select Ports (COM and LPT); select Communications Port (the COM port the sensor is connected to); select Port Settings; select Advanced; move the arrows on both Receive and Transmit Buffers to their lowest settings. Then click OK. This should correct the problem.
Slider 10. Will the 4- 20 mA or 1-5 VDC work with a PLC that is sink or source?
Yes, as long as the proper wiring is in place as shown below:
What standard continuous pressure transmitter ranges are offered by Madison Company?
0 – 2.5 PSIG to 0 – 150 PSIG, and custom models can be configured to read up to 300 PSI. Stock models are designed for tanks and other low pressure applciations to read continuous fluid levels typically 0 to 5 PSI range (0 to 11.5ft water tanks / well water levels) Ses our stock PH4201-005-P025 model.
What pressure units does Madison commonly calibrate sensors to?
- PSI (pounds per square inch)
- Inches of H2O (1" H2O = 0.0361 PSI. Also, 1.0 PSI = 27.68" of H2O)
What agency approvals do these products meet?
Standard models come with CE approvals, but others can be manufactured with FM agency approvals for hazordous locactions and applications.
What does long-term stability mean? How does it affect the measurements?
Long-term stability is normally associated with the change in zero offset due to aging of component and relaxation of the metallic diaphragm over a period of time. It normally causes the zero reading to go high or low over time. Independent tests carried out on these products have shown this number to be 25% under the influence of temperature and pressure cycling for 1500 hours.