calServer Architecture Overview¶

calServer is a calibration management software platform built on a web-based architecture. It is designed to manage measurement equipment, calibration processes, certificates, and customer relationships for calibration laboratories and industrial organizations.

This page describes the technical architecture of calServer, its components, and typical deployment scenarios.

System Architecture¶

calServer uses a multi-tier web architecture:

┌──────────────────────────────────────────────────────────┐
│                      Clients                              │
│                                                          │
│  ┌──────────┐  ┌──────────────┐  ┌────────────────────┐  │
│  │ Browser  │  │ Customer     │  │ External Systems   │  │
│  │ (Desktop,│  │ Portal       │  │ (ERP, MET/CAL,     │  │
│  │  Mobile) │  │ (Browser)    │  │  custom software)  │  │
│  └────┬─────┘  └──────┬───────┘  └────────┬───────────┘  │
│       │               │                   │              │
└───────┼───────────────┼───────────────────┼──────────────┘
        │               │                   │
        ▼               ▼                   ▼
┌──────────────────────────────────────────────────────────┐
│                    Web Server                             │
│              (Apache / Nginx + PHP)                       │
│                                                          │
│  ┌────────────────────────────────────────────────────┐  │
│  │              Application Layer                      │  │
│  │                                                    │  │
│  │  ┌──────────────┐  ┌────────────────────────────┐  │  │
│  │  │ Web UI       │  │ REST API                   │  │  │
│  │  │ (Frontend)   │  │ (JSON endpoints)           │  │  │
│  │  └──────────────┘  └────────────────────────────┘  │  │
│  │                                                    │  │
│  │  ┌──────────────┐  ┌────────────────────────────┐  │  │
│  │  │ Certificate  │  │ Business Logic             │  │  │
│  │  │ Generator    │  │ (Calibration workflows,    │  │  │
│  │  │ (PDF/Report) │  │  scheduling, audit trail)  │  │  │
│  │  └──────────────┘  └────────────────────────────┘  │  │
│  └────────────────────────────────────────────────────┘  │
│                                                          │
└───────────────────────────┬──────────────────────────────┘
                            │
                            ▼
┌──────────────────────────────────────────────────────────┐
│                    Database Server                         │
│           (MySQL / PostgreSQL / SQL Server)                │
│                                                          │
│  • Equipment records    • Calibration results            │
│  • Customer data        • Audit trail                    │
│  • Order information    • System configuration           │
│  • Certificate data     • User and role management       │
└──────────────────────────────────────────────────────────┘

Core Components¶

Web-Based Frontend¶

calServer runs entirely in the web browser. No client-side software installation is required. The frontend provides:

Equipment inventory management with search, filtering, and categorization
Calibration management including scheduling, result entry, and status tracking
Order management for commercial calibration laboratories
Dashboard with key metrics and pending tasks
Administrative interfaces for system configuration

REST API¶

calServer exposes a REST API that enables integration with external systems. The API uses JSON for data exchange and supports:

Equipment data — Create, read, update instrument records
Calibration results — Submit measurement data from external calibration systems
Orders — Create and manage calibration orders programmatically
Status queries — Check calibration status of specific instruments
Certificate retrieval — Download generated calibration certificates

The REST API enables integration with calibration execution software (e.g., MET/CAL), ERP systems, and custom laboratory automation.

Database Storage¶

calServer supports multiple database backends:

Database	Status
MySQL	Fully supported
PostgreSQL	Supported
Microsoft SQL Server	Supported

The application uses database-agnostic access patterns, allowing deployment on the database platform preferred by the organization. All database access is abstracted through the application's ORM and query builder layers.

Certificate Generation¶

calServer generates calibration certificates as PDF documents. The certificate engine:

Uses configurable report templates
Populates certificates with calibration data, measurement results, and instrument identification
Includes measurement uncertainty where applicable
Supports laboratory branding (logos, headers, footers)
Generates unique certificate numbers
Supports digital signatures

Data Separation¶

calServer separates data on two levels:

One installation per customer. Every installation, self-hosted or hosted, has its own database. Several companies with separated data in one shared installation (multi-tenancy in the strict sense) is not something calServer currently provides.
Customer-based visibility within an installation. A user only sees the customers assigned to them, together with those customers' equipment and contacts. Who may see everything is governed by the customer_global and inventory_global permissions.

Integration Points¶

calServer integrates with external systems at several points:

Integration	Method	Purpose
Calibration execution software	MET/TEAM and MET/CONNECT synchronization, REST API	Take over measurement results from Fluke MET/CAL, connect other systems through the REST API
ERP systems	REST API / Data export	Synchronize orders, customers, and invoicing data
LDAP / Active Directory	LDAP protocol	User authentication and single sign-on
Email systems	SMTP	Notifications for calibration deadlines, order updates
Barcode / QR scanners	Web interface	Equipment identification using barcode labels
Instrument communication	via MET/CAL	calServer does not control instruments itself; automated measurements run in MET/CAL and the results arrive through the MET/TEAM or MET/CONNECT synchronization

Not included: environmental monitoring. calServer prints a target range on the calibration certificate and accepts actual values on the record, but it monitors nothing and connects to no monitoring system (EmonCMS).

Typical Deployment Scenarios¶

On-Premises Deployment¶

The laboratory hosts calServer on its own infrastructure:

Web server and database server within the organization's network
Full control over data, security, and access
Suitable for laboratories with strict data sovereignty requirements
IT department manages updates, backups, and infrastructure

Hosted / Cloud Deployment¶

calServer is hosted by a service provider or in a cloud environment:

Reduced infrastructure management overhead
Access from any location with internet connectivity
Service provider handles system maintenance and backups
Suitable for laboratories without dedicated IT infrastructure

Hybrid Deployment¶

Combination of on-premises and hosted components:

Core system on-premises for data control
Customer portal accessible externally
API endpoints available for external integrations
Balances data sovereignty with accessibility requirements

Security Considerations¶

Authentication — User authentication with support for LDAP/SSO integration
Authorization — Role-based access control with configurable permissions
Audit trail — Changes to the core objects (equipment, calibrations, customers, orders, repairs, locations, documents, prices) are logged field by field with user and timestamp; scope and limits under Audit Trail
Data isolation — One database per installation; within an installation, customer-based visibility
Transport security — HTTPS encryption for all client-server communication
Backup — Database backup procedures for data protection